Synchronous inverter

ABSTRACT

An apparatus includes a first inverter circuit and a second inverter circuit. The first invertor circuit is configured to couple an alternator and a load device to deliver a driving signal from the alternator to the load device. The second invertor circuit is configured to couple the alternator to the load device to deliver a driving signal from the alternator to the load device and configured to couple a battery to the alternator to deliver a charging signal from the alternator the battery

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation under 37 C.F.R. § 1.53(b) of U.S.patent application Ser. No. 16/182,130 filed Nov. 6, 2018 (AttorneyDocket No. 10222-15004E), which is a continuation of U.S. patentapplication Ser. No. 15/843,833 filed Dec. 15, 2017 (Attorney Docket No.10222-15004D), which is a continuation-in-part of U.S. patentapplication Ser. No. 15/287,485 filed Oct. 6, 2016 (Attorney Docket No.10222-15004C), which is a continuation-in-part of U.S. patentapplication Ser. No. 15/175,761 filed Jun. 7, 2016 (Attorney Docket No.10222-15004B), which is a continuation-in-part of U.S. patentapplication Ser. No. 14/885,112 filed Oct. 16, 2015 (Attorney Docket No.10222-15004A). The entire disclosures of each are hereby incorporated byreference.

FIELD

This application relates to the field of variable speed generators, andmore specifically, an alternating current (AC) to AC converter forcontrolling the output of a controlled-field synchronous alternator on avariable-speed generator.

BACKGROUND

An engine-generator set, which may be referred to as a generator or agenset, may include an engine and an alternator or another device forgenerating electrical energy or power. One or more generators mayprovide electrical power to a load through a power bus. The power bus,which may be referred to as a generator bus or common bus, transfers theelectrical power from the engine-generator set to a load. In manyexamples, the electrical load on the engine-generator set may vary overtime.

The frequency of the output of a synchronous generator is based on thespeed of the engine and the number of poles in the generator. In orderto provide a constant output frequency, the prime mover may have tooperate at a fixed speed. The engine may not need to operate at thefixed speed in order to provide enough power to supply the load, butdoes so to maintain frequency.

Although allowing the engine speed to decrease at light loads may reducewear, fuel consumption, and sound emissions from the generator,converting the frequency is required in order to allow the engine speedto decrease from rated speed.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are described herein with reference to thefollowing drawings.

FIGS. 1A and 1B illustrate example engine-generator sets including oneor more synchronous inverters.

FIG. 2 illustrates an example single phase segmented waveform converter.

FIGS. 3A and 3B illustrate example switches for the segmented waveformconverter.

FIG. 4 illustrates an example three phase segmented waveform converterwith alternator field current control.

FIG. 5 illustrates another example three phase segmented waveformconverter.

FIG. 6A illustrates an example pin diagram for an integrated circuit forthe segmented waveform converter of FIG. 4.

FIG. 6B illustrates an example pin diagram for an integrated circuit forthe segmented waveform converter of FIG. 5.

FIG. 6C illustrates an example power supply for supplying current to thealternator field.

FIGS. 7A and 7B illustrate example single phase wiring diagrams forsynchronous inverters.

FIG. 8A illustrates an example low wye wiring diagram for synchronousinverters.

FIG. 8B illustrates an example high wye wiring diagram for synchronousinverters.

FIG. 9 illustrates an example low delta wiring diagram for synchronousinverters.

FIG. 10 illustrates a synchronous inverter generator configured to crankthe engine using the alternator and synchronous inverter.

FIG. 11A illustrates an example engine torque curve.

FIG. 11B illustrates an example power curve for an engine.

FIG. 12A illustrates a chart for alternator losses in an examplecontrolled field alternator on a variable speed generator containing asynchronous inverter.

FIG. 12B illustrates an example engine speed versus load curve andsystem loss curves for a system including a synchronous inverter.

FIG. 13 illustrates an example side view of a dual axis generator.

FIG. 14 an example block diagram for an example synchronous invertersystem.

FIG. 15 illustrates a block diagram for another example synchronousinverter system.

FIG. 16 illustrates an example controller.

FIG. 17 illustrates a flow chart for the controller of FIG. 15.

FIG. 18 illustrates an example alternator and two synchronous inverters.

FIG. 19 illustrates an example alternator and three synchronousinverters.

FIG. 20 illustrates an example lawnmower implementing a synchronousinverter for battery charging.

FIG. 21 illustrates an example lawnmower implementing three synchronousinverters in addition to a synchronous inverter for battery charging.

FIG. 22 illustrates an example lawnmower implementing three synchronousinverters and a utility source.

FIG. 23 illustrates an example lawnmower implementing synchronousinverters and supplemental synchronous inverters for battery chargingand a utility source.

FIG. 24 illustrates an example lawnmower and a utility source.

FIG. 25 illustrates an example vehicle including synchronous inverters.

FIG. 26 illustrates an example vehicle including synchronous invertersin addition to a synchronous inverter for battery charging.

FIG. 27 illustrates an example vehicle including synchronous invertersand a utility source.

FIG. 28 illustrates an example generator system including a synchronousinverter system.

FIG. 29 illustrates an example generator system including a synchronousinverter system for providing power from the generator in addition to asynchronous inverter for providing power from a battery.

FIG. 30 illustrates another example generator system with a synchronousinverter.

FIG. 31 illustrates a flow chart for the operation of the generatorcontroller of FIG. 16.

FIG. 32A illustrates an example engine-generator sets including asynchronous inverter and an external load device.

FIG. 32B illustrates an example engine-generator sets including asynchronous inverter and a motor.

FIG. 33 illustrates an example vehicle including a synchronous inverterand at least one motor.

FIG. 34 illustrates an example subassembly for the vehicle of FIG. 33.

FIG. 35 illustrates a reverse view of the example subassembly of FIG.34.

FIG. 36 illustrates a top view of the example subassembly of FIG. 34.

FIG. 37 illustrates a perspective view of the vehicle.

FIG. 38 illustrates a flow chart for powering a vehicle with asynchronous inverter.

FIG. 39 illustrates an example set of inverters for driving a motor in awye configuration.

FIG. 40 illustrates an example set of inverters for driving a motor in adelta configuration.

FIG. 41 illustrates a hybrid arrangement of a set of inverters fordriving a motor.

FIG. 42 illustrates a hybrid arrangement of a set of inverters fordriving a load.

FIG. 43 illustrates a simplified hybrid arrangement of a set ofinverters for driving a motor.

FIG. 44 illustrates another simplified hybrid arrangement of a set ofinverters for driving a motor.

FIG. 45 illustrates an example of the motor of FIGS. 41-44.

FIG. 46 illustrates an example battery mode for hybrid operation of amotor.

FIG. 47 illustrates an example engine mode for hybrid operation of amotor.

FIG. 48 illustrates an example maximum power mode for hybrid operationof a motor.

FIG. 49 illustrates an example crank while driving mode for hybridoperation of a motor.

FIG. 50 illustrates an example regenerative mode for hybrid operation ofa motor.

FIG. 51 illustrates an example maximum braking mode for hybrid operationof a motor.

FIG. 52A illustrates a vehicle and a series drive system for theinverter.

FIG. 52B illustrates a vehicle and a parallel drive system for theinverter.

FIG. 53 illustrates an example light tower application for the inverter.

FIG. 54A illustrates a marina application for a series drive system forthe inverter.

FIG. 54B illustrates a marina application for a parallel drive systemfor the inverter.

FIG. 55 illustrates an example doubly fed machine using the inverter.

FIG. 56 illustrates an example a flow chart for operating the doubly fedmachine.

FIG. 57 illustrates a load banking device.

DETAILED DESCRIPTION

An alternating current (AC) to AC converter converts an AC signal orwaveform to another AC signal having a different or changed electricalproperty. The changed electrical property may be voltage, frequency, oranother property. Example types of AC to AC converters includecycloconverters, matrix converters, and hybrid converters. Acycloconverter converts the input waveform to a lower frequency outputsignal by synthesizing segments of the input waveform without a directcurrent link. Cycloconverters may use silicon controlled rectifiers(SCRs) as switches to synthesize the inputs. Matrix converters utilize anetwork of transistors to similarly synthesize segments in a piecewisemanner in order to generate the desired output waveform. Hybridconverters may combine a combination of the two approaches. Althoughfrequency converters or cycloconverters may allow for correction of thefrequency, they operate to control the output of the generator withoutcontrol of the input.

Any of these examples may be referred to collectively as a segmentedwaveform converter. The segmented waveform converter may generate asingle phase output from a multiple phase input. The output of thesegmented waveform converter may be a four-quadrant output as thesegmented waveform converter can transfer both real power and reactivepower in either direction through the segmented waveform converter. Thesegmented waveform converter generates the output waveform one segmentat a time by directly passing a combination of one or more of the inputsignals. Appropriate filtering of the input waveform may be used toremove high-frequency ripple, switching noise, and undesirabledistortion of the output. The output waveform is created from sequentialpiecewise sampling of the input voltage. The frequency of the samplingdefines the length of the segments. The frequency of the sampling may besignificantly higher than the frequency of the input waveform and theoutput waveform. For example, an input frequency of 200 Hz and an outputfrequency of 60 Hz may require a sampling and switching frequency of 20kHz in order to provide acceptable output power quality.

An additional advantage realized from the segmented waveform converter,as opposed to conventional inverters, is that lower rated components maybe used. The segmented waveform converter uses more switching elementsbetween the source and load than conventional rectifiers. Thus, onaverage, less current must go through each of the switching elements,and the switching elements may have a smaller current or power rating.Lower rated components may be much less costly. The segmented waveformconverter may be electrically connected to one or more filters andconfigured to provide a filtered output to a variety of loads. Such asegmented waveform converter may be referred to as a synchronousinverter herein.

It is preferred to allow the cycloconverter to control the input voltageand frequency in addition to the output voltage in order to optimizeefficiency and provide protection for components in the cycloconverter.In addition, many cycloconverters generate total harmonic distortion(THD) on the output voltage due to switching and commutation noise. ThisTHD can be undesirable depending on the application.

FIG. 1A illustrates an example engine-generator set 10 a including asynchronous inverter 11, an engine 12, and an alternator 13. Thesynchronous inverter may include at least one controller (i.e.,microprocessor) for controlling a network of switches of a segmentedwaveform converter. The alternator 13 may be a controlled fieldalternator in which a field current is actively controlled by agenerator controller (field current controller) to adjust the output ofthe alternator 13. The synchronous inverter controller and the fieldcurrent controller may be the same device or different devices. Theoutput device 14 of the synchronous inverter provides the outputwaveform to a load or another device.

The controlled field alternator 13 is configured to generate apoly-phase signal through operation of the engine 12. The controlledfield alternator 13 may include an exciter armature for generating afield current. As the exciter armature is rotated in a magnetic flux, atime varying voltage is induced in the windings of the exciter armature.The output from the exciter armature is connected to the main fieldportion of generator. The connection may be made with or without brushesand slip rings. The field current of the output of the exciter providesa magnetic field in rotor field of the generator. As the field portionof the alternator is rotated relative to the stator, a magnetic flux ispassed through and across the alternator stator windings producing timevarying voltage. The field current from the exciter armature output maybe rectified or otherwise controlled.

The output of the alternator 13 may be a three phase signal. The phasesof the poly-phase signal may be offset one another by a predeterminedangle (e.g., 120 degrees or 2*Pi/3 radians). The poly-phase signal mayvary with respect to amplitude and frequency.

The controlled field alternator 13 provides the poly-phase signal to thesegmented waveform converter of the synchronous inverter 11, which mayinclude a matrix cycloconverter. The segmented waveform converterincludes a network of switches that selectively controls passing acombination of the components of the poly-phase signal to the output 14.For example, consider an example in which the poly-phase signal includestwo components, A and B. The network of switches could provide severalcombinations of the two components to the output, which may include onlythe A component, only the B component, an additive signal of A+B, asubtracted signal of A−B or B−A, and 0 or a null signal, which may beachieved by A−A or B−B.

Before the output 14, the synchronous inverter 11 may include an outputfilter and electrical quantities may be measured by the controller atthe output filter by one or more sensors. The controller of thesynchronous inverter 11 may be configured to provide a control signalfor the network of switches based on measured electrical quantitiesassociated with the output filter and provide a field current controlsignal to the controlled field alternator.

The controller may receive the electrical quantities from at least onesensor. The controller may perform a calculation or consult a lookuptable to determine a combination of the components of the poly-phasesignal to pass to the output 14. In one example, a lookup table relatescombinations of available voltages to different settings for theplurality of switches. The available voltage may change over time. Inone example, the available voltages vary according to a time-basedschedule of expected values. In another example, the available voltagesvary according to measured values.

FIG. 1B illustrates another example engine-generator set 10 b includingtwo synchronous inverters 11 a and 11 b, an engine 12, and an alternator13. The two synchronous inverters 11 a and 11 b may be connected througha synchronization path 15.

Both synchronous inverters 11 a and 11 b are fed by alternator 13 andare configured to synchronize their output waveforms using the syncsignal on the synchronization path 15 between synchronous inverters 11 aand 11 b. The sync signal may include a digital signal which mayindicate a peak, a positive-going or negative-going zero-crossing on thetarget voltage waveform, or another element of the internal targetsignal. The sync signal may include an analog signal, indicating atarget waveform, a phase angle indicator, or another element of thetarget output waveform.

The sync signal may be a communications signal communicating a targetvoltage, target frequency, real load, reactive load, apparent load,zero-crossing timestamp, time synchronization signal, or otherinformation related to the measured output waveform, the target outputwaveform, or the input to the inverter from the alternator. In oneexample, one of the synchronous inverters 11 a detects a zero crossingand slope of the output of synchronous inverter 11 a, which is sent tothe other synchronous inverter 11 b using the sync signal. The othersynchronous inverter 11 b may introduce a delay in order to synchronizewith the synchronous inverter 11 a. Various techniques may be used tosynchronize the synchronous inverters.

The supplies from the alternator 13 to the synchronous inverters 11 aand 11 b may be magnetically isolated from each other to allowconnection of the inverters in series, the two inverters may allow forconnection in a center-tap configuration, allowing 120 or 240 outputvoltage as desired. FIG. 2 illustrates an example synchronous inverter11 including segmented waveform converter 20. The segmented waveformconverter 20 includes a network of switches SW1-6 and at least oneenergy storing device. The example shown in FIG. 2 includes an inductor21 and a capacitor 23. The inputs, A, B, and C, to the segmentedwaveform converter 20 are components of the poly-phase AC waveforms.

In one example, the segmented waveform converter 20 is configured tosupply a control signal to each of the switches for any combination oftwo or fewer of the components of the poly-phase input waveform. Thecontrol signal may include A, B, C, A−B, A−C, B−C, B−A, C−B, C−A, and 0.Other switch configurations may be configured to provide othercombinations, such as additive combinations A+B, B+C, and A+C, using aswitch configuration other than that illustrated. In another example,the segmented waveform converter 20 is configured to supply apredetermined set of outputs based on combinations of the components ofthe poly-phase input waveform. The predetermined set of outputs mayinclude a subtractive combination of exactly two of the components,including A−B, A−C, B−C, B−A, C−B, and C−A. The predetermined set ofoutputs may include 0, any single component (A, B, or C) or anysubtractive combination of exactly two of the components.

The controller may access a target output level as a function of time.For example, the target output may be an AC waveform at a specificfrequency and/or a specific amplitude. The target output level may bestored as a series of time based target values. For example, time valuesare associated with target output levels (e.g., {time1, output1},{time2, output2}). The target output level may follow a sinusoidalfunction, and the target output levels may be computed based on aspecified voltage and frequency for the output.

The controller may calculate a target electrical parameter for theoutput filter. In one example, the controller calculates a targetcurrent for the inductor 21, and in another example, the controllercalculates a target voltage for the capacitor 23. The controller maycalculate a desired change in the electrical parameter based on ameasured quantity (e.g., voltage or current) at the output filter. Thecontroller may calculate a change value (delta) based on the differencebetween the target output level and the current measured quantity. Thecontroller may compare the change values to the available outputsegments from the combinations of components and selects the closestcombination.

TABLE 1 Time A-B B-C C-A B-A C-B A-C Target 1 49 163 −212 −49 −163 212110 2 −80 −135 215 80 135 −215 168 3 −197 173 24 197 −173 −24 18 4 201−25 −176 −201 25 176 −150 5 −94 230 −136 94 −230 136 −170 6 196 −189 −7−196 189 7 −75

Different switch combinations correspond to different output ranges. Forexample, at time interval 3 on Table 1, combination C−A provides 24V,which is closest to the target at time interval 3 (18). In anotherexample, at time interval 2, combination C−B provides 135, which is theclosest to the target at time interval 2 (168). For each time interval,the controller selects one of the possible combinations. Only sixcombinations are shown, but more combinations are possible. A lookuptable based on a single phase measurement may be used. Alternatively,each phase may be measured and compared. The controller may compare thepossible combinations to the target value and select the closestcombination. The controller generates a field current control signal forthe selected combination. The controller may output an individualcontrol signal for each of the switches SW1-6. Each switch SW1-6 may beeither on or off. Each of the combinations represents different currentpaths through the segmented waveform converter.

As another example, the controller may select the switch combinationthat provides that largest voltage to the output and determine a pulsewidth modulated (PWM) duty cycle to operate between that switchcombination and a free-wheeling state. The PWM duty cycle may be chosenbased on a ratio between the target voltage and the available voltage, apredetermined sequence, a closed-loop output voltage controller, amodel-based control of the output, or a similar technique.

The controller may determine whether the closest available combinationis within a threshold difference to the target. When the closestavailable combination is farther away from the target than thethreshold, the controller may apply PWM control to adjust the signal.For example, a PWM duty cycle may be applied to the closest combinationto approach the target. In another example, when the closest availablecombination is farther away from the target than the threshold, thecontroller first selects the available combination that is greater thanthe target. Then, the controller applies a PWM duty cycle to adjust theselected combination to approach the target. The PWM duty cycle may becalculated according to Equation 1.

PWM Duty Cycle=Target/Selected Combination Output  Eq. 1.

For example, consider the example at time interval 2, combination C−Bprovides 135, which is the closest to the target at time interval 2(168). The controller may revert to the next largest output (215) fromcombination (C−A). Using Equation 1, the PWM duty cycle would be(168/215)=0.78 or 78%. In one example, the PWM duty cycle may be finelytuned (e.g., every 1%). In another example, a few examples are availableand the closest PWM duty cycle is selected. For example, when five dutycycles are available, the options may be 20%, 40%, 60%, 80%, and 100%.In the example above, when equation 1 provides 78%, the PWM duty cycleof 80% is selected.

Table 2 illustrates example control signals for each of the switches inorder for the segmented waveform converter 20 to provide the variousoutput levels or combination of components of the poly-phase signal. Thecontroller may include an output pin for each of the switches to providethe individual control signals to the switch. In another example, thesegmented waveform converter 20 may include a switch controller thatreceives a bitwise signal according to rows of Table 2. For example,each series of bits corresponds to a set of control signals in theformat {SW1, SW2, SW3, SW4, SW5, SW6}.

TABLE 2 SW1 SW2 SW3 SW4 SW5 SW6 A-B 1 0 0 0 1 0 A-C 1 0 0 0 0 1 B-C 0 10 0 0 1 B-A 0 1 0 1 0 0 C-B 0 0 1 0 1 0 C-A 0 0 1 1 0 0 0 or A-A 1 0 0 10 0 0 or B-B 0 1 0 0 1 0 0 or C-C 0 0 1 0 0 1

The controller may calculate a target electrical parameter for theoutput filter. In one example, the controller calculates a targetcurrent for the inductor 21, and in another example, the controllercalculates a target voltage for the capacitor 23. The controller maycalculate a desired change in the electrical parameter based on ameasured quantity (e.g., voltage or current) at the output filter. Thecontroller calculates a change value (delta) based on the differencebetween the target output level and the measured quantity. Thecontroller compares the change values to the available output segmentsfrom the combinations of components and selects the closest combination.

The filter components Inductor 21 and capacitor 23 may be selected tominimize THD on the output of the inverter. They may also be selectedbased on a target switching frequency of the segmented waveformconverter. The filter components may be replaceable or integral to thedesign. The filter components may be different based on target outputvoltages and frequencies from the inverter. As an example, the inductor21 may be decreased in size when the output frequency increases. Asanother example, the capacitor may be increased in size for a lowervoltage application. The filter components may vary by application, suchas decreased filter size when feeding a motor load or increased filtersize when feeding a sensitive load.

The filter components may also enable the inverter to controlshort-circuit current by limiting the rate that the current through theswitch can rise. The current control may provide a sinusoidal,trapezoidal, saw-tooth, triangular, DC, square-wave or otherwise shapedoutput current into a short circuit. The frequency of the output currentinto a short circuit may differ from nominal frequency. The currentcontrol may provide a high level of output current slowly decreasing toa lower level of output current. As an example, the current control mayprovide 300% of rated generator current into a short circuit for 2seconds, then decrease the output current to 100% of rated current overthe next 5 seconds. As another example, the current control may provide300% of rated generator current into a short circuit for 5 seconds, thenstop sourcing current.

FIG. 3A illustrates example switches SW1-6 for the segmented waveformconverter 20. The switches SW1-6 include a pair of transistors 25 (e.g.,metal-oxide-semiconductor field-effect transistors or MOSFETs) which arecontrolled by a gate driver 27 through one or more gate resistors 26.The sources of the transistors 25 may be directly electricallyconnected. The switches may also utilize a plurality of transistorsconnected in parallel in order to increase the current rating or todecrease the losses in the power conversion.

The switches are configured such that they block current traveling ineither direction. This allows the segmented waveform converter to switchbetween two AC waveforms. The body diode, if present, on each transistorcan conduct when the transistor is conducting in one direction, so thevoltage drop across one transistor is typically lower than the other.The gate driver circuit provides the necessary isolation to allow thesources of the switches to float relative to the input and output of theconverter, while providing a voltage or current referenced to thesources to trigger the switch. The gate drivers pass a digital signalfrom the controller to the actual switch.

FIG. 3B illustrates another example switches SW1-6 for the segmentedwaveform converter 20. The switches SW1-6 include a pair of transistors29 (e.g., insulated-gate bipolar transistor (IGBT) or anotherthree-terminal power semiconductor device.) The emitters of thetransistors 29 may be directly electrically connected. The switches mayalso utilize a plurality of transistors connected in parallel in orderto increase the current rating or to decrease the losses in the powerconversion. The emitters may be connected using paralleling resistors ifthe thermal characteristics of the IGBTs are not conducive toparalleling.

The switches are configured such that they block current traveling ineither direction. This allows the segmented waveform converter to switchbetween two AC waveforms. The body diode on each transistor can conductwhen the transistor is conducting in one direction, so the voltage dropacross one transistor is typically lower than the other. The gate drivercircuit provides the necessary isolation to allow the emitters of theswitches to float relative to the input and output of the converter,while providing a voltage or current referenced to the emitters totrigger the switch. The gate drivers pass a digital signal from thecontroller to the actual switch.

FIG. 4 illustrates an example network 30 a of segmented waveformconverters. The inputs to the network 30 a include S1, S2, and S3 forthe first segmented waveform converter, T1, T2, and T3 for the secondsegmented waveform converter, and U1, U2, and U3 for the third segmentedwaveform converter. The outputs of the network 30 include one outputline (L1, L2, L3) for each of the segmented waveform converters. Theenergy storing devices 33, which may be inductors, in combination withenergy storing devices 34, which may be capacitors, combine to form anoutput filter. The measurement points 37, for current, and 39, forvoltage, illustrate example locations on the network 30 where electricalquantities may be measured for controlling the segmented waveformconverters. Other voltage and current measurement locations may beutilized. A circuit 35 includes a field current power supply forgenerating a field current (DC+, DC−) that is transmitted back to thefield coils of the alternator.

In FIG. 4 each of the segmented waveform converters share the neutralconnection (N). Thus, each of L1 and L2 and L3 can be connected only inparallel or in a three-phase wye configuration. FIG. 5 illustratesanother example three phase segmented waveform converter in which eachof the segmented waveform converters are independent and can beconnected in any configuration.

Each of the converters is capable of providing a single-phase AC output,but the phase between the outputs may be fixed such that the network ofconverters produces a poly-phase AC output. For example, the output ofthe three converters, between 1 and 4, 2 and 5, and 3 and 6, may befixed at 120 electrical degrees apart, providing three phase power. Asanother example, the three outputs, between 1 and 4, 2 and 5, and 3 and6, may all produce voltage at the same phase angle, allowing them to beconnected in parallel to provide increased current sourcing capabilityin a single-phase application. In yet another example, one of the threeoutputs, 3 and 6, could produce voltage at 180 electrical degrees fromthe other two, 1 and 4, 2 and 5, allowing center-tap single-phase outputvoltages such as 120/240. In this case, one of the output lines from thegenerator has double the current rating of the other output line becausetwo converters are connected in parallel. In another example, outputs 1and 4 may be 180 electrical degrees from 2 and 5 with 3 and 6 at thesame phase angle as 1 and 4 with twice the magnitude. This enablescenter-tap single-phase output voltages with balanced line currentratings but only half the line current is available from the neutralconnections. This final configuration may require higher voltageswitches for the converter, 31, connected to inputs U1, U2, U3.

FIG. 6A illustrates an example pin diagram for a circuit package orintegrated circuit for a network of segmented waveform converters 30 a.The inputs to network 30 a, which are S1, S2, S3, U1, U2, U3, T1, T2,and T3, are on one side of the circuit package, and the line outputs L1,L2, and L3, neutral line N, and field current outputs DC+, DC− are onthe other side of the circuit package. The controller area network (CAN)provides a control input to the circuit package in order to set theoutput. The control input may be the bitwise switch settings describeabove (e.g., {SW1, SW2, SW3, SW4, SW5, SW6}) or the control input may bea target output, and the switch settings are controlled internal to thecircuit package.

FIG. 6B illustrates an example pin diagram for a similar circuit packageor integrated circuit for the network of segmented waveform converters30 b. The inputs to network 30 b, which are S1, S2, S3, U1, U2, U3, T1,T2, and T3, are on one side of the circuit package, and the differentialoutputs 1, 2, 3, 4, 5, and 6, and field current outputs F+, F− are onthe other side of the circuit package. As described above the CANcontrol input to the circuit package sets the output with either bitwiseswitch settings or a target output level.

FIG. 6C illustrates an example power supply 40 for controlling the fieldcurrent. The field current power supply 40 may be used in combinationwith the circuit of FIG. 5 or in lieu of circuit 35 in FIG. 4. The powersupply 40 includes an array of transistors 41 and a switching powersupply for stepping up the voltage.

The network of waveform converters provides an output to control thefield on the alternator 13, allowing the converters to control supplyvoltage(s). The field on the alternator 13 may be supplied by ahigh-voltage DC bus, generated from battery voltage by a DC−DCconverter. Control of the supply voltage may allow for improvedefficiency, decreased stress on components, broader output voltagerange, and improved control under short-circuit conditions, among otherbenefits.

In any of the examples above, the synchronous inverters may be connectedto provide two equally-rated (e.g., 120V) power supplies or thesynchronous inverters may be connected in a variety of configurations.The inverters are in communication via a synchronization signal betweenthem to allow the inverters to provide synchronized output voltage. Inthis case, the two inverters provide a very versatile range of outputvoltages, allowing a single generator package to be used in a variety ofapplications.

FIGS. 7A and 7B illustrate example single phase wiring diagrams forsynchronous inverters that may be achieved by the segmented waveformconverters of either FIG. 4 or FIG. 5. FIG. 7A illustrates circuitry asa means for connecting a low voltage (e.g. 120 VAC), single-phaseoutput. FIG. 7B illustrates circuitry as a means for connecting anominal voltage (e.g. 220 or 240 VAC) for a single-phase configuration.

FIG. 8A illustrates circuitry as a means for connecting a Low Wye (e.g.120/208 VAC) three-phase configuration that may be achieved by thesegmented waveform converters of either FIG. 4 or FIG. 5. FIG. 8Billustrates circuitry as a means for connecting a High Wye (e.g. 230/400or 277/480 VAC) three-phase configuration that may be achieved by thesegmented waveform converters of FIG. 5. FIG. 9 illustrates circuitry asa means for connecting a center-tap Delta (e.g. 120/240/208 VAC) threephase configuration that may achieve by the segmented waveformconverters of FIG. 5.

FIG. 10 illustrates an example engine-generator set including an engine51, a battery 52, a controlled field machine (CFM) 55, two segmentedwaveform converters 53, and a generator controller 50. Each of thesegmented waveform converters 53 includes a power stage 54, amicroprocessor 56, and a cranking switch 58. The engine 51 includes oris electrically connected with an engine control module (ECM) 57 and acrank angle sensor 59. The power stage 54 includes the array of switchesfor receiving the CFM outputs 61 that feed into the segmented waveformconverters 53 and the field current line 63 to supply field current backto the CFM 55. The CFM 55 may be an alternator or another rotary devicethat is controlled by an electrical field. Additional, different, orfewer components may be included in the genset.

The synchronous inverter 53 may be used to initiate engine rotation(crank the engine 51). The synchronous inverter 53 receives batterypower from battery 52 on the normal AC output and provides an AC voltagewaveform on the alternator stator windings, generating a rotatingmagnetic flux in the stator. The rotating magnetic flux on the statormay generate a torque on the rotor. The generated torque causes theengine to spin, causing air and fuel to be compressed in the cylindersand allowing the engine to initiate combustion (start).

Based on the layout of the segmented waveform converter, the switchesallow for bi-directional power flow. Given this configuration, it may bepossible to provide a signal that allows the alternator to act as amotor to rotate the engine. The alternator may act as an inductionmachine using damper windings in the rotor, induced current in the rotorfield winding, reluctance variation between the rotor and stator,magnetic hysteresis in the rotor, or eddy currents generated in therotor steel or laminations. The alternator may also act as a synchronousmachine by exciting the rotor field, by rectifying induced voltage inthe rotor field, or providing a permanent magnet rotor. The rotor fieldmay be excited by an AC voltage, a DC voltage, or a combination of ACand DC voltage. The rotor field supply may couple through the exciterarmature when the rotor is stationary.

The generator controller 50 is configured to provide a start signal tothe segmented waveform converter 53. In addition to the start signal,the segmented waveform converter 53 may receive a position signal of therotational components relative to the stationary components to determinethe speed and position of the engine. In some cases, the position signalmay provide information to the segmented waveform converter 53 thatallows the synchronization of the AC voltage applied to the alternatorstator. The segmented waveform converter may also determine engineposition by measuring back electromagnetic fields (EMF) from the statorwindings, stator impedance, stator current, or another signal. In somecases, the output of the crank angle sensor 59 (an angle) may be feddirectly into the synchronous inverter 53. In other cases, the crankangle sensor 59 may be read by the ECM 57 or generator controller 50 andthe information communicated to the synchronous inverter 53.

The engine cranking may be performed by one or more of the segmentedwaveform converters. The converters may share the cranking loadsimultaneously, share the cranking load by switching convertersoccasionally, or some combination of the two techniques. The converterto supply the cranking current may be chosen based on a temperature ofeach converter, the time that the converter has supplied the current, inorder to assess functionality of the components on each converter, orfor another reason.

The engine cranking may also be performed by a separate converter or athree-phase inverter. The separate inverter may be part of the segmentedwaveform converters or a separate converter. The separate converter mayconnect to a dedicated set of windings on the alternator. The dedicatedset of windings on the alternator may be galvanically isolated from thewindings connected to the segmented waveform converters. The dedicatedset of windings may have a different number of turns than the mainwindings. The dedicated set of windings may be used to recharge thebattery that supplies the cranking current.

The engine cranking may be performed by controlling the frequency andamplitude of the applied voltage. The engine cranking may be performedby controlling the voltage and phase angle between the rotor and stator.The engine cranking may be performed by controlling the torque appliedto the engine 51. The torque applied to the engine can be measured fromthe phase angle between the current and voltage, the amplitude of thecurrent, the amplitude of the voltage, the engine speed, or othercharacteristics of the stator or rotor.

FIG. 11A illustrates a chart for engine gross torque for an exampleengine-generator set including a synchronous inverter. As shown by plot110, the engine provides increasing torque as the speed increases formost of the operating speed of the engine. Due to the torque outputlimitations of the engine, it may be difficult to accelerate the enginequickly from a lower speed. In addition, accelerating from a lower speedmay take longer because of the infrequency of combustion events.

The engine torque produced may be significantly less than is indicatedin FIG. 11A, depending on the torque demanded by the alternator. Theengine output torque may be controlled by controlling the fuel supply tothe engine. The engine output torque may be controlled by controllingthe air supply to the engine. The torque demanded by the alternator mayincrease with increasing electrical load. The engine speed may decreaseif the alternator torque exceeds the engine torque produced. The enginespeed may increase if the engine torque exceeds the alternator torque.The alternator torque may have to be limited to a level slightly belowthe engine torque in order to allow the engine to accelerate.

FIG. 11B illustrates a chart for engine power for an exampleengine-generator set including a synchronous inverter. As shown by plot112, the engine speed may increase in order to provide enough power tomeet the load demand. The engine speed may be controlled by controllingthe torque output of the engine. In order to allow the engine speed toincrease, the synchronous inverter may have to reduce output voltagetemporarily. If the engine is unable to provide enough power to supplythe load, the inverter may have to reduce output voltage temporarily.

The engine may operate at a fixed speed, with the output voltagecontrolled by adjusting the field current. The engine may operate at avariable speed with the output voltage controlled by adjusting theengine speed. The engine may operate at a combination of fixed speed andvariable speed, with the output voltage controlled by a combination ofadjusting the speed and adjusting the field current. The outputfrequency of the alternator may be controlled by adjusting the enginespeed. The synchronous inverter may increase the frequency of the outputvoltage from that of the alternator. The synchronous inverter maydecrease the frequency of the output voltage from that of thealternator. Different alternator and engine types require differentmeans of controlling the input voltage to the synchronous inverter.

The synchronous inverter may control the output from the alternator inorder to control the input voltage to the segmented waveform converter.Control of the alternator output may provide improved protection forswitches in the converter, decreased THD on the output, improvedefficiency, better durability, and improved response.

FIG. 12A illustrates a chart 114 for rotor and stator losses in analternator on an example engine-generator set including a synchronousinverter. The example design uses a wound-field alternator to producethe voltage supply to the synchronous inverter and an ECM that allowsadjustment of the engine speed. The rotor losses in the alternator maybe at a maximum at low speed because the alternator is operating insaturation at low speed in order to allow maximum voltage generation ata minimum speed. The stator losses may increase due to increasing copperlosses from current due to increasing load. The total losses may be at amaximum at no load because the system efficiency is not important at noload. The system losses may be at a minimum at 30% load because 30% loadis the most common operating point for the generator.

FIG. 12B illustrates a chart 116 for total system losses for an exampleengine-generator set including losses from the synchronous inverter. Theexample generator set may be rated to produce 10 kW. The total systemlosses may be approximated by the sum of the alternator and inverterlosses. The total efficiency may be computed as the ratio between thetotal power provided by the alternator to the total power produced bythe engine. The example generator set may have an efficiency approaching90%.

As illustrated in FIG. 12B, the engine speed increases with increasinggenerator load. This may allow the engine to provide sufficient power tosupply the load and may also improve fuel consumption, sound and airpollutant emissions, and system longevity. The engine speed may remainconstant, decrease or increase in a different example. The alternatorvoltage produced by the system may increase with increasing load, remainconstant, or decrease with increasing load. Increasing alternatorvoltage with increasing load may help to minimize THD, constant voltagewith changing load may simplify inverter control, and decreasing voltagewith increasing load may help to minimize stress on components in thesegmented waveform converter.

FIG. 13 illustrates an example wound-field alternator to provide voltageto the synchronous inverter. The example alternator is configured withthe exciter field lying in a common plane with the main machine. Theexample alternator topology may provide additional voltage control andimproved speed range over a permanent magnet alternative. The examplealternator topology may provide a similar size profile and efficiency toa permanent magnet alternative. The example alternator topology may beintegral to the flywheel of the engine. In this example, the outputshaft of the engine may drive a coolant pump, a fan, a fuel pump,another device, or be removed from the shaft casting. The output sealmay also be removed from the end-plate casting of the engine.

FIG. 13 illustrates a shaft 222 that supports a rotor frame 223. Astator frame 221 is supported by a fixed member that provides the frameof reference for the rotating rotor. The fixed member may be an engineblock or skid or other fixed member. The rotor frame 223 rotates withthe shaft. The rotor frame 223 supports a rotor field device and anexciter armature device 224 d. Thus, the rotor field device 224 a andthe exciter armature device 224 d may be rigidly mounted together orintegrally formed. The stator frame 221 supports an exciter field device224 c, and a main stator device 224 b. Thus, the exciter field device224 c and the main stator device 224 b are rigidly mounted in the sameframe of reference relative to the rotor or may be integrally formed.Either or both of the stator side and the rotor side may be formed ofcast iron or steel or laminated silicon steel or other magneticallypermeable materials. The outermost component may be designed to act as ashield for electromagnetic interference due to high frequency switchingof a power electronic device or devices interior to the outermostcomponent. Also, this may be designed to minimize radiatedelectromagnetic interference conducted to the alternator from anexternal power electronic device such as a synchronous inverter.

An exciter air gap 225 a is maintained between the exciter field device224 c and the exciter armature device 224 d. The exciter field device224 c is energized by a voltage regulator or another power source togenerate an exciter magnetic field in the exciter air gap 225 a. Theexciter armature device 224 d is configured to rotate with respect tothe exciter field device 224 c and impart a first time varying voltagein a set of coils in the exciter armature across the exciter air gap 225a. In one alternative, the exciter field device 224 c may includepermanent magnets. In another alternative, the exciter field device mayinclude coils or another magnetic field generating device.

A main air gap 225 b is maintained between the rotor field device 224 aand the main stator device 224 b. The main stator device 224 b includesa second set of coils. The rotor field device 224 a is configured to beenergized by the first current in the first set of coils and generate amain magnetic field that imparts a second time varying voltage in thecoils of the main stator device 224 b across the main air gap 225 b.

As illustrated in FIG. 13, the main stator device 224 b and the exciterfield device 224 c lie in on a common plane normal to an axis ofrotation of the shaft 222. In a first embodiment, only the main statordevice 224 b and the exciter field device 224 c lie in on the commonplane with the rotor field device 24 a and the exciter armature device224 d lying in an adjacent plane. In this example, the adjacent planeincluding the rotor field device 224 a and the exciter armature device224 d are axially spaced from the main stator device 224 b and theexciter field device 224 c. In this embodiment, the main air gap 225 band the exciter air gap 225 a lie in adjacent planes or a common planenormal to the shaft. In this first embodiment, magnetic flux travelsparallel to the axis of shaft rotation across the main airgap 225 b andthe exciter airgap 225 a. In a another embodiment, the main statordevice 224 b, the exciter field device 224 c, the rotor field device 224a and the exciter armature device 224 d lie in the common plane. In thisembodiment, the main air gap 225 b and the exciter air gap 225 a may beconcentrically aligned parallel to the axis of the shaft 222 with all orpart of the cylindrical exciter air gap 225 a contained within thecylindrical main air gap 225 b. The exciter armature device 224 d isinwardly spaced from the exciter field device 224 c, main stator device224 b, and the rotor field device 224 a. In other words, the exciterarmature device 224 d is closer to the shaft 222 than the exciter fielddevice 224 c, the main stator device 224 b, and the rotor field device224 a. In this second embodiment, magnetic flux travels normal to theaxis of shaft rotation across the main airgap 225 b and the exciterairgap 225 a. Note combinations of the first and second embodiments arepossible and contemplated.

FIG. 14 illustrates a block diagram for an example synchronous invertersystem. The example synchronous inverter contains three segmentedwaveform converters 205 a, 205 b and 205 c which may provide thepotential to produce three-phase output power through the filtercircuits 207 a, 207 b, and 207 c. The segmented waveform converters 205a, 205 b and 205 c may be supplied with controlled voltages S1, S2, S3,T1, T2, T3, U1, U2 and U3 from the alternator 13 through the inputfilters 201 a, 201 b, and 201 c. The input voltages S1, S2, S3, T1, T2,T3, U1, U2 and U3 may be adjustable using the field current controldevice 216. The field current control device 216 may be circuitry or adevice configured to receive a command or control signal from themicrocontroller 200 and generate a field current in response to thecommand. The control signal or command for field current control device216 may be generated by the microcontroller 200. The segmented waveformconverters may be controlled based on the input metering 203 a, 203 band 203 c and the output metering 209 a, 209 b and 209 c. The segmentedwaveform converters may be controlled by the microcontroller 200.

The cranking battery voltage may be applied to the segmented waveformconverters 205 a-c through the filters 207 a-c by switching outputcontactors 202 a-c. The synchronous inverter may provide engine crankingcapability using the segmented waveform converters 205 a-c to provide athree-phase AC voltage on the alternator windings. Voltages S1, S2 andS3, T1, T2 and T3 and U1, U2 and U3 may be galvanically isolated fromeach other. Voltages S1, S2 and S3, T1, T2 and T3 and U1, U2 and U3 maybe connected to separate windings in the alternator 13.

The cranking battery 218 may be charged from the inputs C1, C2 and C3from the alternator 13. The voltage generated on C1, C2 and C3 may begalvanically isolated from the voltage generated on S1, S2, S3, T1, T2,T3, U1, U2, and U3. The voltage provided to C1, C2 and C3 may begenerated by a separate winding in the alternator 13. The batterycharger 213 may receive a rectified DC voltage from C1, C2 and C3through the rectifier 211. The battery charger 213 may be controlledbased on a fixed sequence. The fixed battery charging sequence mayinclude a bulk charge mode where the voltage is maintained at a higherlevel until the current drops below a threshold, a float mode where thevoltage is maintained at a low enough level to avoid overcharging thebattery and an equalize mode where the voltage is increased for a shortduration to ensure that the charge in all cells in the battery is equal.The battery charger 213 may be controlled based on the battery metering215. The battery charger 213 may be controlled by the microcontroller200. The microcontroller 200 may be powered by the board power supply217. All components on the synchronous inverter may be switched at thesame frequency to minimize electromagnetic interference (EMI) due toaliasing of the signals.

The input filters 210 a-c may provide protection to the switches in thesegmented waveform converters 205 a-c in addition to the snubbercircuits provided with the switches. In addition, the input filters 201a-c may provide a bypass path for the current flowing through theinductance of the output windings supplying S1, S2, S3, T1, T2, T3 U1,U2 and U3, allowing the current to be switched as necessary to minimizethe THD of the output voltage.

The output filters 207 a-c may provide a bypass for the high-frequencyswitching noise from the segmented waveform converters 205 a-c. Themicrocontroller 200 may determine the voltage on the output and thecurrent in the filter inductor using the output metering 209 a, 209 band 209 c. The microcontroller 200 may determine the output current fromthe inverter based on the filter inductor current, the voltage on thefilter capacitor, the switching position, past information from avariety of signals, and system parameters such as the capacitance of thefilter capacitor and the inductance of the filter inductor. Themicrocontroller 200 may determine the capacitance value of the filtercapacitor over time. The microcontroller 200 may learn the inductance ofthe filter inductor over time. The output metering 209 a, 209 b and 209c may include measurement of the output current.

The microcontroller 200 may determine a real and reactive droopcharacteristic based on the computed or measured output current fromeach inverter. The real and reactive droop characteristic may be used tooperate seamlessly in parallel with a standard generator. The real andreactive droop characteristics may allow for parallel operation withanother generator using a synchronous inverter. The output of thegenerator may be protected outside the four-quadrant capability curvefor the generator by opening all switches, closing all switches, somecombination thereof, or some other function of microcontroller control.

FIG. 15 illustrates an example synchronous inverter topology thatprovides a segmented waveform converter on C1, C2 and C3 to crank theengine. The example is similar to that illustrated in FIG. 14 with theaddition of the fourth segmented waveform converter 205 d, as well ascorresponding input filter 201 d, input meter 203 d, output filter 207d, and output metering 209 d, and the removal of output contactors 202a-c. The additional segmented waveform converter 205 d may provide thecapability of sourcing AC output voltage from the generator withoutrunning the engine if a magnetic flux is applied to the stator withoutexciting the rotor field. The magnetic flux applied to the statorthrough windings C1, C2 and C3 may generate a voltage on windings S1,S2, S3, T1, T2, T3, U1, U2, and U3 of the alternator 13. This capabilitymay require different alternator topology such as the ability todisconnect the rotor field from the exciter armature or rectifier andthe removal of any damper or induction windings in the rotor.

When cranking battery voltage is applied to segmented waveformconverters 205 a-c, the synchronous inverter may crank the engine. Thecrank sequence may be initiated by a digital signal, a communicationssignal, a state of existing inputs and outputs, or by the presence ofcranking battery voltage on the outputs as detected by the outputmetering 209 a, 209 b and 209 c. Cranking may be controlled by themicrocontroller 200. Cranking may be performed by measuring a phaseangle of the alternator rotor and moving a magnetic flux to a positionat a given angle away from the rotor position. Cranking may becontrolled by measuring a speed of the alternator rotor and rotating amagnetic flux at a given difference in speed, also called slipfrequency. Cranking may my controlled by providing a fixed rotationfrequency in a known direction without feedback from the engine.

Combining the control of input voltage and frequency within the samesynchronous inverter that provides the output voltage and frequency mayprovide various advantages. As an example, the synchronous inverter mayprovide 139 VAC line to neutral in order to produce 240 VAC line to linein a low-wye configuration or 480 VAC line to line in a high wyeconfiguration. Providing this additional voltage may require increasedinput voltage from the alternator, but such increased voltage may beunnecessary when providing 120 VAC line to neutral to produce 208 VACline to line. Including control of the engine speed may allow thesynchronous inverter to improve the efficiency of the system byminimizing the engine speed or improve efficiency by providing afrequency that is an integer multiple or simple ratio to the desiredoutput frequency. In addition, control of the engine speed may allow thesynchronous inverter to adjust voltage outside the range otherwiseprovided by adjusting the field current. As an example, the alternatormay only be able to produce 90 VAC at 1000 RPM, but 100 VAC may berequired to produce 139 VAC line to neutral. In this case, thesynchronous inverter may increase the engine speed to 1100 RPM in orderto provide 100 VAC.

The alternator field current may be provided by a battery, the AC outputof the generator, a dedicated coil on the alternator, or a combinationof sources. The synchronous inverter may control the field current usinga half bridge supply or a full bridge supply. The half bridge supply maybe capable of providing positive voltage to the field and allowing it todecay naturally. The full bridge supply may be able to provide anegative and positive voltage to the field, increasing and decreasingthe current more quickly. The half-bridge driver may be provided withbattery voltage or with a higher voltage generated from the batteryvoltage or another source. The full-bridge driver may be provided withbattery voltage or with a higher voltage generated from the batteryvoltage or another source.

Combining engine starting capability into the synchronous inverter mayallow the total system complexity to be reduced by utilizing the samecomponents for both operations and eliminating the need for a separatestarting motor. Starting using the alternator may provide quieterstarting operation by removing the power transfer through spur gears onthe starter motor and flywheel, lower current draw on the crankingbattery by improved efficiency, reduced wear on the system due tominimized side loading while cranking, higher cranking speed due tolower loss connection, decreased package size and lower cost due toremoval of the dedicated starting motor, and galvanic isolation due tothe use of separate windings in the alternator from the battery chargingwindings.

Integrating battery charging in the inverter may decrease total packagesize by eliminating the battery charging alternator, improve reliabilityof the system by removing the drive mechanism for the battery chargingalternator, reduce system complexity by eliminating one controller,provide galvanic isolation between the battery and the generator outputsby using a separate winding, and provide a high-voltage supply for thefield from the battery charging windings.

The alternator 13 may have inductance in the stator which may causevoltage spikes on the input to the segmented waveform converter. Thevoltage spikes that are generated by the inductance may be minimized bythe input filter, by control algorithms for the segmented waveformconverters, and by control of the alternator field and engine speed.

The output of the synchronous inverter may be used to operate a motor,similar to a variable frequency drive operation. The segmented waveformconverter topology may allow for bi-directional power transfer from themotor, allowing regenerative breaking from the motors. If multiplemotors are being driven by a given generator, power may be transferredfrom one motor to the other.

The alternator may have slightly varying characteristics withtemperature and manufacturing tolerance stackup. The microcontroller inthe inverter may adapt to the changing characteristics to allow forconsistent operation between all products utilizing the synchronousinverter configuration. The engine performance characteristics may alsovary with atmospheric conditions, manufacturing tolerances, fuel typesand maintenance items. The microcontroller may be able to adapt to theengine characteristics in order to provide expected power quality overthe entire load range.

The microcontroller 200 may control the output voltage using closed-loopfeedback from the output metering. The microcontroller 200 may controlthe output voltage as a function of the input voltage. The voltage maybe controlled with a combination feedback and feed-forward system, withfeed-forward tables that may provide adaptive learning capability.

In a short circuit condition, the microcontroller 200 may control theoutput current using closed loop feedback from the output metering. Theoutput filter inductor may limit the rise rate of the output current,potentially protecting the switches from damage when sourcing into ashort-circuit condition. The short circuit current may be controlled bythe switches in the segmented waveform converters, the excitation levelin the alternator, or a combination of the two. In addition the outputcurrent may be controlled in a scenario where the inverter is connectedto a motor in order to limit motor torque.

In cases were multiple inverters are used, the inverters may communicatea synchronizing signal in order to match phase angle across differentinverters. The synchronizing signal may be provided over communications,a digital signal, and analog signal, or by observation of the inputvoltage from the alternator, among other techniques. The sync signal mayprovide loading information, target information, control mode,connection information, etc. If multiple inverters are used, only oneinverter may have control of the field current. That said, the otherinverter(s) in the system may want to adjust their supply voltage, sothe inverters may communicate a desired input voltage over thecommunications network, a digital signal or an analog signal.

If multiple inverters are used in parallel, the inverters may need toshare loading information in order to equalize the load on eachinverter. This may be provided by communications, digital signals,analog signals, or simple droop handling.

The output voltage from different inverters may be tied in parallel withother inverters, or even multiple output stages from a single invertermay be connected together. The configuration of the output of theinverter may be user-adjustable or it may automatically detect thatoutputs are connected together in order to determine how to control thevoltage. Automatic connection detection could involve a specific powerup sequence where one inverter stage observes voltage on the input, itcould involve current monitoring for abnormalities, it could involvetransmission of a special signal on the outputs to be received byanother device, or another technique.

FIG. 16 illustrates an example generator controller 91. The generatorcontroller 91 may include a processor 300, a memory 352, and acommunication interface 353. The generator controller 91 may beconnected to a workstation 359 or another external device (e.g., controlpanel) and/or a database 357 for receiving user inputs, systemcharacteristics, and any of the values described herein. Optionally, thegenerator controller 91 may include an input device 355 and/or a sensingcircuit 311. The sensing circuit 311 receives sensor measurements fromas described above (e.g., alternator output SWC output). Additional,different, or fewer components may be included. The processor 300 isconfigured to perform instructions stored in memory 352 for executingthe algorithms described herein. The processor 300 may be compatiblewith a variety of engine and alternator combination and may identify anengine type, make, or model, and may look up system characteristics,settings, or profiles based on the identified engine type, make, ormodel. FIG. 17 illustrates a flow chart for the operation of thegenerator controller of FIG. 16. Additional, different of fewer acts maybe included.

At act S101, the processor 300 accesses from memory 352 or from realtime measurement (e.g., sensing circuit 311), a measured electricalquantity at an inverter output. The inverter output may be an actualpower signal applied to a load under a specification. The specificationmay be a target value for a sinusoidal signal at time intervals.Alternatively, the target value may specify an amplitude range or rootmean squared range for the inverter output. The target value may specifya variance or quality (e.g., THD) level for the inverter output.

At act S103, the processor 300 calculates a change value for based onthe measured electrical quantity and the target value. In other words,the processor 300 determines the difference between the target value andthe actual value of the inverter output. The change value may be eitherpositive or negative.

At act S105, the processor 300 compares the change value to availableinverter inputs. One set of available inverter inputs is shown on eachrow of Table 1 above. The available inverter inputs depend on either theexpected or actual values of outputs of the alternator. For example, ina three phase alternator having outputs A, B, and C, the set of outputsmay be A, B, C, A−B, B−C, A−C, B−A, C−B, and C−A. Each of the set ofoutputs has a value, which changes on each time interval (e.g., samplinginterval).

At act S107, the processor 300 selects a closest available inverterinput combination (alternator output) based on the comparison. In oneembodiment, the closest available inverter input combination is usedwithout modification. In another embodiment, the closest availableinverter input combination is modified to more closely achieve thetarget value using PWM.

At act S109, the processor determines a switch setting for a switcharray of a segmented waveform converted corresponding to the selectedinverter input combination. The switch setting is a digital signal orseries of bits that describes which of the switches of the segmentedwaveform converter should be turned on and off in order to provide theselected inverter input combination.

At act S111, the processor 300 provides a waveform to the inverteroutput corresponding to the switch setting. In one example, theprocessor 300 calculates a difference between the closest availableinverter input combination and the target value, and modifies thewaveform using a pulse width modulated signal with a duty cycle that isbased on the difference between the closest available inverter input andthe target value.

FIG. 18 illustrates an example system including an engine 401, analternator 403, two synchronous inverters or segmented waveformconverter 405 a and 405 b, an output device 400, and a battery 413. Oneof the synchronous inverters 405 a is coupled with a motor 407 a, abrake 409 a, and a wheel 411 a, and the other of the synchronousinverters 405 b is coupled with a motor 407 b, a brake 409 b, and awheel 411 b. Either or both of motors 407 a and 407 b are examples of anoutput drive mechanism for the system. The motors 407 a and 407 b may bereferred to individually and interchangeably as motor 407, the brakes409 a and 409 b may be referred to individually and interchangeably asbrake 409, and the wheels 411 a and 411 b may be referred toindividually and interchangeably as wheel 411. The engine 401 maydirectly drive the output device 400. Additional, different, or fewercomponents may be included.

The alternator 403 is mechanically coupled with the engine 401. Asdescribed in earlier embodiments, the rotation of an output shaft of theengine 401 rotates an exciter portion and a main field portion of thealternator 403. The exciter portion includes an exciter armature forgenerating a field current to induce a time varying magnetic flux in thearmature windings, generating voltage. The induced voltage in thewindings of the exciter armature is connected to the main field portionof generator. The corresponding field current of the output of theexciter provides a magnetic field in rotor field of the main fieldportion of the generator. As the main field portion of the alternator isrotated relative to the stator, a magnetic flux is passed through andacross the alternator stator windings producing an alternator outputsignal in bus 402. Alternate forms of field control are included hereinas well (e.g. brushes and slip rings, flux weakening coils, direct axiscurrent injection).

The alternator output signal may include multiple components that areselectively controlled by the synchronous inverters 405 a and 405 b. Thederivation of the output of the synchronous inverters 405 a and 405 b,or the conversion of the alternator output signal to the output of thesynchronous inverters 405 a and 405 b may be performed by generatorcontroller 50, generator controller 91, or microcontroller 200 (any onereferred to individually as “controller”) in the examples describedpreviously. The controller may consult a lookup table or a configurationvalue that is specifically tailored to a particular type of motorapplication of the motor, or feedback based on the current operation ofthe motor. The controller may determine switch settings for multiplesettings that set the output of the synchronous invertors as combinationof the multiple components of the alternator output signal. One of thecomponents may be passed or multiple components may be added orsubtracted. The controller may apply the switch settings to at least onesegmented waveform converter including multiple switches connectedbetween the alternator 403 and the output drive mechanism (e.g., motors407 a and/or 407 b).

The motors 407 a and 407 b may be AC motors comprising a stationarystator including coils supplied with alternating current by thesynchronous inverters 405 a and 405 b (referred to individually or assynchronous inverter 405). The coils induce a rotating magnetic fieldthat causes a rotor and attached to an output shaft of the AC motor torotate. The stator and rotor may be housed in a casing, and the statormay be mechanically coupled to the casing. The output shaft may berotatably mounted to the casing using a bearing.

The output of the synchronous inverter 405 may include a drive frequencythat causes the output shaft of the motor to rotate at a particularspeed. In one example, the speed of the output shaft in rotations persecond is the same as the drive frequency in cycles per second orrelated by a predetermined ratio. In other examples, as with inductionmotors, the drive frequency and shaft speed may not be related by apredetermined ratio. The predetermined ratio may depend on the numbersof poles in the rotor and/or the number of poles of the stator.

The output of the synchronous inverter 405 may be selected, via switchsettings, to cause the speed of the output shaft to change in time. Thechanges in the speed of the output shaft may be within a time intervalthat is less than a single rotation of the output shaft or even lessthan a cycle of the output of the synchronous inverter 405, which may bereferred to as electrical subcycle torque control. Electrical subcycletorque control applies in torque changes to the output shaft in lessthan an electrical cycle of the output of the synchronous inverter 405.Electrical subcycle torque control may be on the order of 1 to tens ofmilliseconds. In this way, very quick changes may be applied to theoutput shaft. The shaft may rotate at multiple speeds within just a fewrotations or even a single rotation.

The controller may select the output of the synchronous inverter 405based on a feedback signal for the rotation of the output shaft, aninput signal, or both. The input signal may be from an input device forsetting the speed of the rotor. The feedback signal may be generated bya sensor such as a rotation sensor. The rotation sensor maymagnetically, optically or mechanically measure the rotation of theoutput shaft. Thus, the feedback signal may be indicative of the speedof the output shaft.

Also, the feedback signal could be derived from the output of thesynchronous inverter 405. The controller may calculate shaft outputcharacteristics such as speed or torque as a function of the synchronousinverter output voltage or current. The controller may compare thefeedback signal to the input signal. When the input signal indicates aspeed or torque for the output shaft that is greater than a speed ortorque target, the controller decreases the frequency, voltage, orcurrent output of the synchronous inverter 405. Likewise, when the inputsignal indicates the speed for the output shaft that is less than thetarget, the controller increases the frequency, voltage, or currentoutput of the synchronous inverter 405.

Through the synchronous inverter 405, the speed of engine 401 andalternator 403 may be independent of the frequency applied to the motors407 and accordingly, independent of the speed of the wheels 411.Therefore, the engine 401 and alternator 403 may be controlled only tooptimize the output device 400 (e.g., speed of the output device) andthe synchronous inverters 405 control the speed of the motors 407. Onlythe alternator 403 power or voltage output is controlled to sufficientlysupply the synchronous inverters.

The speed of the engine 401 and the output of the synchronous inverters405 may be independent within an operating range of the engine 401.Through the operating range, the output device 400 speed may be adjustedwithout interrupting the speed applied to the motors 407 and the wheels411. In other words, when the engine 401 is operated within apredetermined power range or rotational speed range, the speed of wheels411 may be operating in any predetermined speed range in which the powerrequirements are met by the predetermined power range of the engine 401.

The battery 413 is connected to the synchronous inverter 405 to act as asource and sink of power. The synchronous inverter 405 may be configuredto charge the battery 413 or utilize the battery 413 as a source ofpower to crank the engine 401 via the alternator 403. The synchronousinverter 405 may also use the battery 413 in a limited capacity todeliver power to the motor 407 or actuate the brake 409. The system iscapable of transferring power between components without use of thebattery. The battery capacity may not be sufficient to provide fullpower to all components.

Power may also travel in the reverse direction, from the motor 407 tothe synchronous inverter 405. For example, a reverse torque may beapplied to motor 407 a, which induces a reverse current though thesynchronous inverter 405 a to the alternator 403. Through the power bus402, the reverse current may contribute to the power drawn by thesynchronous inverter 405 b and applied to motor 407 b.

In one example, the system illustrated in FIG. 18 is applied to avehicle such as a forklift, a loader, a golf cart, or a lawnmower suchas a zero turn radius lawnmower. A zero turn radius lawnmower may be alawnmower in which at least two wheels are individually controlled.While the term “lawnmower” may be used in some of the followingembodiments, substitutes may be made for other types of vehicles. Asidefrom the deck and mower apparatus, the drive systems and synchronousinventors may be applied to other types of vehicles. Thus, each wheel411 a and 411 b are individually controlled by the outputs of thesynchronous inverters 405 a and 405 b. A first segmented waveformconverter 405 a is associated with a first wheel 411 a of a vehicle anda second segmented waveform converter 405 b is associated with a secondwheel 411 b of the vehicle. The first wheel 411 a and/or the secondwheel 411 b is coupled to a drive train, which is the output drivemechanism (primary drive system), to propel the vehicle. In alternativeembodiments, only a single wheel is controlled, multiple wheels areconnected to a single motor, or three or more motors for multiple wheelsare controlled.

Advantages of electrical control using the synchronous waveformconverters may be realized over hydraulic or other mechanical systems.For example, in addition to the increased granularity of torque control,electrical drive is more efficient than hydraulic systems. Theefficiency improvements save in fuel costs and a smaller engine may beselected. Electrical systems have other advantages over hydraulicsystems including the elimination of hydraulic fluid spills, which maydamage equipment or vegetation.

The lawnmower may also include a mowing system. The mowing systemincludes one or more blades configured to cut grass or other vegetation.The mowing system may correspond to output device 400. A shaft, belt orother drive train may mechanically connect the engine 401 to the outputdevice 400. The output device 400 and the engine 401 may respond to thepower requirements of cutting depending on the specific localrequirements (e.g., thickness of the vegetation, water content, or otherfactors).

In operation, when the vehicle is traveling generally in a straight linethe speed of the wheels is the same. However, when making turns, theinner wheel with respect to the curve or turn experiences a loweraverage speed or number of revolutions than the outer wheel with respectto the curve or turn. For the slower wheel to reduce speed, a brake 409may be applied to the wheel 411. In addition, a power transfer (e.g.,negative torque, reverse torque, rear facing torque) may be made fromthe inner wheel to the outer wheel. The kinetic energy of the rotatingmass of the inner wheel is consumed to deliver power to the outer wheel,thereby effecting a braking force on the inner wheel while effecting anaccelerating force on the outer wheel without drawing power from or assupplement to power delivered by the engine. As an example, the kineticenergy of the rotating mass of the inner wheel 411 a is used to drivethe motor 407 a to generate power, controlled by synchronous inverters405 a, which is delivered via bus 402 to synchronous inverters 405 b fordrive of the outer wheel 411 b. In a further embodiment, the powerdelivered by the inner wheel synchronous inverters 405 a may be used tocharge battery 413 or battery 505.

In one example, the controller is configured to generate and provide amagnetic field control signal to the controlled field alternator 403.The magnetic field control may adjust the field current. Alternatively,an armature reaction technique such as adjustment of current on fluxweakening coils or a mechanical technique such as changing a linkagepath of the magnetic path may be used to modify the magnetic flux or themagnetic field control signal. In other examples, a DC output from atleast one of the segmented waveform converter may be applied to thecontrolled field alternator 403 as a field current. The DC output may begenerated by circuit 35 described in other embodiments. The magneticfield control may be provided by one or more of the synchronous inverterDC outputs. Alternatively, the magnetic field control may be provided byanother device with or without a signal from the synchronous inverters405.

The DC output of the other synchronous inverter may be applied to arelease mechanism for the brakes 409. The primary function of the brakesis to slow the wheels 411 when activated. However, the brakes 409 mayinclude a safety mechanism (e.g., a spring) that defaults to biasing thebrakes 409 to stop the vehicle. The safety mechanism may be released byan actuator (e.g., solenoid) when so signaled by the DC output of thesynchronous inverter. This causes the brakes to be applied when theengine 401 or the synchronous inverter is off and to be released whenthe engine 401 or the synchronous inverter is running and applying theDC output.

The DC output of the other synchronous inverter may be applied toanother purpose such as a control panel, safety mechanism, or statusindicator. The control panel may include an interface for setting theoutput of the synchronous inverter. The safety mechanism may be acircuit to measure an electrical quantity of the synchronous inverterand compare to a threshold and identify an error with the threshold isexceeded. The status indicator may include one or more lights ordisplays that indicates the synchronous inverter. In another embodiment,the DC output of the other synchronous inverter may be used to power anaccessory outlet or lighting of a configurable AC or DC nature.

FIG. 19 illustrates an example alternator and three synchronousinverters for a lawnmower. Similar components illustrated previously areconsistent with FIG. 19. Additional, different or fewer components maybe included.

FIG. 19 includes a third synchronous inverter 405 c that controls athird motor 407 c for the mower 410 (e.g., mower deck). Thus, the outputdrive mechanism (secondary drive system) coupled with the synchronousinverter 405 c drives the mower 410. In this embodiment, the engine 401only drives the alternator 403. Control of engine speed and torque maybe made solely on total power requirements of the system, which may bebalanced and allocated by the synchronous inverters 405. In other words,cutting speed for the mower 410 is independent of engine speed and thespeed of each of the wheels 411 is independent of the engine speed. Aswell, the cutting speed for the mower 410 may be independent of thespeed of each of the wheels 411 (e.g., wheel 411 a is independent ofmower 410, wheel 411 b is independent of mower 410, and wheel 411 a isindependent of wheel 411 b). In the embodiment of FIG. 19, any of the DCoutputs of the synchronous inverters 405 may supply the field current tothe alternator 403. In one example, the magnetic field control isprovided by synchronous inverter 405 c that drives the mower 410.

FIG. 20 illustrates an example lawnmower implementing a synchronousinverter for battery charging. The engine 401 in the embodiment of FIG.20 directly drives the mower 410. Similar components illustratedpreviously are consistent with FIG. 20. Additional, different or fewercomponents may be included.

A synchronous inverter 503 (supplemental segmented waveform converter),which may also be configured and operated by the controller, appliedpower from battery 505 to the power bus 402, and accordingly, tosynchronous inverters 405 and the motors 407. Power may also flow in thereverse direction. That is, when braking or otherwise slowing one of thewheels 411, the motor 407 may act as a generator and provide power backto synchronous inverter 503 to charge the battery 505. Therefore, eitherof synchronous inverters 405 a and 405 b may charge the battery 505.

A switch 501, which may be implemented as a relay or an additionsynchronous inverter, connects and disconnects the alternator 403 to thepower bus 402. The switch 501 may also be operated by the controller.

At accessory output 507 provided by the synchronous inverter 503 maypower other electrical systems or accessories of the lawnmower. Theother accessories may include headlights, gauge panels, turn signals,horns, radios, or other devices.

FIG. 21 illustrates an example lawnmower implementing three synchronousinverters in addition to a synchronous inverter for battery charging.Similar components illustrated previously are consistent with FIG. 21.Additional, different or fewer components may be included.

In this embodiment, synchronous inverter 405 c provides power to motor407 c, which drives mower 410. In addition, the DC output of thesynchronous inverter 405 c may set the height of deck 610 of the mower410. The controller may receive a user input for deck height (e.g.,distances from the ground) and in response, control the switch settingsof synchronous inverter 405 c to raise or lower the deck 610 usinganother motor or drive mechanism.

FIG. 22 illustrates an example lawnmower implementing three synchronousinverters and a utility source. Similar components illustratedpreviously are consistent with FIG. 22. Additional, different or fewercomponents may be included.

The embodiment of FIG. 22 includes a utility source that may alsoprovide power to the power bus 402 through synchronous inverters 613 aand 613 b. Any number of synchronous inverters may be coupled to theutility source 615. The utility may be an AC source provided to thelawnmower through a variety of delivery mechanisms. In one example, anelectrical cord may extend to the vehicle from the utility (e.g.,electrical outlet). Alternatively, an inductive or other wirelesscoupling may provide the utility source 615. For example, one or moreinductive coils may be buried or otherwise placed beneath a drivingsurface. The inductive coils induce a voltage on one or more receivingcoils in the lawnmower and provide power to the synchronous inverters613 a and 613 b, which are configured and operated by the controller.

FIG. 23 illustrates an example lawnmower implementing synchronousinverters for the drive of the motion of the lawnmower, mowing of thelawnmower, and supplemental synchronous inverters for charging thebattery 505 and the utility source 615. Similar components illustratedpreviously are consistent with FIG. 23. Additional, different or fewercomponents may be included.

Depending on the circumstances or current settings, the utility source615, the battery 505 and/or the alternator 403 may provide power to thewheels 411 a and 411 b through synchronous inverters 405 a and 405 band/or the mower 410 and/or deck 610 through the synchronous inverter405 c. Also depending on the circumstances or current settings, theutility source 615 and/or the alternator 403 may charge the battery 505through the synchronous inverter 603.

FIG. 24 illustrates an example lawnmower and a utility source and noengine. Similar components illustrated previously are consistent withFIG. 24. Additional, different or fewer components may be included.

Depending on the circumstances or current settings, the utility source615 and/or the battery 505 may provide power to the wheels 411 a and 411b through synchronous inverters 405 a and 405 b and/or the mower 410and/or deck 610 through the synchronous inverter 405 c. Also dependingon the circumstances or current settings, the utility source 615 maycharge the battery 505 through the synchronous inverter 603.

The battery 505 may also provide power to an external device such as alight tower. For example, at some times the utility source 615 chargesthe battery 505 when the utility (e.g., induction coils) are nearby, andwhen the lawnmower is remote from the utility source 615, the battery505 provides power to the external device.

FIG. 25 illustrates an example vehicle including synchronous inverters.Two synchronous inverters 405 are shown, but more or fewer can be usedto power motor 707. In the case of more than one synchronous inverter405, they would be operated in parallel to increase power capacity,increase voltage, increase redundancy, or for improved controllability.Similar components illustrated previously are consistent with FIG. 25.Additional, different or fewer components may be included. Theembodiment of FIG. 25 may be a lawnmower but is not a zero turn radiuslawnmower. The vehicle includes the engine 401, the alternator 403, oneor more synchronous inverters 405 a and 405 b, a motor 707 coupled withwheels 711, a manual brake 703, an emergency brake 705, and an output710. The wheels may be connected to the motor directly or via a torqueconverter (e.g. gear reduction, differential). A steering mechanismturns wheels 711 together. As described in earlier embodiments, powertransfer may occur in a forward direction from the alternator 403,through the synchronous inverters 405, to the motor 707, and ultimatelyto wheels 711. An output of one of the synchronous inverters 405 mayprovide the output 710, which may be converted from DC to AC (e.g., 120V convenience output).

FIG. 26 illustrates an example vehicle including synchronous invertersin addition to a synchronous inverter for battery charging. Similarcomponents illustrated previously are consistent with FIG. 26.Additional, different or fewer components may be included.

As described in earlier embodiments, bidirectional power transfer mayoccur in a forward direction from the alternator 403, through thesynchronous inverters 405, to the motor 707, and in a reverse directionfrom the wheels 711 in response to either emergency brake 705 or manualbrake 703 being applied, through the synchronous inverters 405 and 603 ato the battery 505.

Rather than the manual brakes in the embodiment of FIG. 25, a brake 805provides stopping capability in addition to the stopping capabilityprovided in a regenerative control scheme. In the regenerative mode, themotor 707 supplies power through the synchronous inverter 405 to thealternator 403, the battery 505, either output 710 or 507, or anycombination thereof.

FIG. 27 illustrates an example vehicle including synchronous invertersand the utility source 615. Depending on the circumstances or currentsettings, the utility source 615, the battery 505 and/or the alternator403 may provide power to the wheels 711 through synchronous inverters405 a and 405 b. Also depending on the circumstances or currentsettings, the utility source 615 and/or the alternator 403 may chargethe battery 505 through the synchronous inverter 603.

FIG. 28 illustrates an example generator system including a synchronousinverter system. Similar components illustrated previously areconsistent with FIG. 28. Output 710 is a DC output and output 721 is anAC output. Through the synchronous inverters 405 a and 405 b, the engine401 may run at variable speeds while providing a constant AC output 721.

FIG. 29 illustrates an example generator system including a synchronousinverter system for providing power from the generator in addition to asynchronous inverter for providing power from a battery. Similarcomponents illustrated previously are consistent with FIG. 29. Eachsynchronous inverter system may provide a DC output. Synchronousinverters 603 a and 603 b provide DC output 810 b, and synchronousinverters 403 a and 403 b provide DC Output 810 a.

FIG. 30 illustrates another example generator system with synchronousinverter. Similar components illustrated previously are consistent withFIG. 30.

The capacitor bank 823 may adapt the single phase utility from utilitysource 615 for the synchronous inverters. The capacitor bank 823generates a poly-phase signal from the single phase utility throughphase shifting the single phase source. The difference in phase isutilized to provide poly-phase input to the synchronous inverter 403.The capacitor bank 823 may include two or more capacitors, or two ormore sets of capacitors to convert single phase source to a three phasesignal. The single phase utility source may be designated as phase A,the output of a first capacitor or first set of capacitors may bedesignated as phase B, and the outputs of a second capacitor or secondset of capacitors may be designated as phase C.

FIG. 31 illustrates a flow chart for the operation of the generatorcontroller of FIG. 16. Additional, different of fewer acts may beincluded.

At act S201, the processor 300 identifies a polyphase signal at acontrolled field alternator (e.g., alternator 403). The polyphase signalmay be detected by the sensing circuit 311.

At act S203, the processor 300 determines determining an output controlsignal for at least one synchronous inverter to control switchesconnected between the polyphase signal of the controlled fieldalternator and at least one output device. The output control signaldetermines the output of the at least one synchronous inverter.

At act S205, the processor 300 determines an output torque for the atleast one output device. The output device may be a wheel, a drivemechanism, a mowing system, a deck height system, or a generator. In analternative embodiment, the processor 300 may determine an output speed,position, or other target for the at least one output device.Additionally, the controlled field alternator may be utilized as theelectrical power source or electrical power may be supplied by analternative source (e.g. utility, battery, wind, solar, nuclear).

Referring to FIGS. 14 and 15, one or more segmented waveform converters205 including a plurality of switches connected to the polyphase signalof the controlled field alternator and configured to generate producethree-phase output power through an output filter circuit including atleast one output filter 207. The output power may be referred to as adrive signal, which may drive at least one motor, as described in theexamples of FIGS. 24-31. An input circuit to the segmented waveform,which may include input filter 201, includes an input coupled to acontrolled field alternator and configured to receive a polyphase signalfrom the controlled field alternator. At least one output filter 207 isconfigured to modify the drive signal based on at least one setting forthe motor. The controller 200 is configured to generate a control signalto set states of the switches to generate the drive signal for the atleast one motor. The control signal may be based on sensor data.

Referring to FIG. 32A, an example engine-generator assembly 70 includesa synchronous inverter 11, an engine 12, an alternator 13, and an outputfilter 74 and is coupled to a load device 65. The synchronous inverter11 may include an input coupled to a controlled field alternatorconfigured to receive a polyphase signal from the controlled fieldalternator and at least one controller (i.e., microprocessor) forcontrolling a network of switches of a segmented waveform converterconnected to the polyphase signal of the alternator 13 and generate adrive signal for at least one load device 75. In addition, thealternator 13 may be a controlled field alternator in which a fieldcurrent is actively controlled by a generator controller (field currentcontroller) to adjust the output of the alternator 13.

Electrical noise from the alternator, in which the waveform deviatesfrom an ideal sinusoidal, becomes mechanical noise (audio) as thewaveform powers the motor. In AC to AC converters, noise is typicallynot a design concern. On heavy equipment such as mining equipment,mechanical noise from electrical motors may be acceptable with respectto cost, because other noise in the environment often exceeds that ofthe electrical motors. Other applications may require that less noise isproduced by the electric motors. In some examples, the sound from thehydraulics may exceed that of the engine. Sounds becomes a priority insome applications such as carts or lawnmowers that are used in quietenvironments such as golf courses. The output filter 74 reduces noise onthe waveform output from the alternator 12, which may include audiblenoise and electromagnetic interference. The output filter 74 may alsoreduce heating in the motor because the filtered waveform more closelymatches the physical characteristics of the motor.

The output filter 74 is configured to modify the drive signal based onat least one setting for at least one load device 75. The output filter74 may include one or more active components include an SCR, a fieldeffect transistor (FET), and an insulated gate bipolar transistor(IGPT), and one or more passive components such as capacitors,inductors, and resistors. The at least one setting may include physicalparameters of the load device 75, a tilt setting for traveling on anincline, a decline, or along an incline, a turn setting for low radiusturns, a load setting for the motor, a fuel efficiency setting, or aconfiguration setting. The following sections each of these examples inmore detail. As shown in FIG. 32B, the at least one load device 75 maybe a motor such as a direct current (DC) motor, an AC induction motor, asynchronous AC motor, a brushless DC motor, a brush-type DC motor, or acombination of multiple of the foregoing designs.

A controller 71 configured to generate a control signal to set states ofthe plurality of switches to generate the drive signal for the at leastone motor. The control signal may be based on sensor data. Examples ofsensor data include lever steering sensor data, load sensor data, ororientation sensor data.

The power system apparatus includes a synchronous inverter and at leastone motor driven by the synchronous inverter. In one example, thesynchronous inverter drives one or more wheels of a vehicle. The powersystem may include multiple synchronous inverters each electricallycoupled with a different electric motor. In addition, the power systemmay include multiple motors driven by a single inverter.

The power system apparatus may include an electric hybrid power systemfor a lawnmower or another vehicle. The electric hybrid power system mayinclude a synchronous invertor and electric motor for each of multipledrive wheels. The electric motors and drive wheels may be drivenindependently according to the techniques described herein. The hybridpower system may include at least one battery that is charged by thealternator at one time or part of a power cycle and later powers atleast one motor at a second time or part of the power cycle.

FIG. 33 illustrates an example vehicle 80 including a synchronousinverter and at least one motor. The vehicle 80 includes the engine 12,alternator 13, and synchronous inverter 11. The vehicle 80 may alsoinclude the output filter 74. The vehicle 80 includes a motor 81, a geartransmission 82, a wheel linkage 83, one or more idle wheels 84, one ormore driven wheels 85, a flywheel 88 on a driveshaft 89 (FIG. 35), and asubframe including a support frame 86 and a gear frame 87. The motor 81may be a direct current (DC) motor controlled by voltage or analternating current (AC) motor controlled by frequency. Additional,different, or fewer components may be included.

The synchronous inverter and at least one motor are an examplealternative to replace a hydraulic propulsion system such as used onzero turn radius (ZTR) lawnmowers. The hydraulic propulsion systemindependently operates two driving mechanisms and drive wheels.Traditional ZTR lawnmowers may include hydraulic valves to controlhydrostatic transmissions driven by belts from an internal combustionengine, which may be fueled by gasoline, diesel fuel, liquefiedpetroleum (LP), compressed natural gas (CNG), or another type ofcombustible fuel. The hydrostatic transmissions require regularmaintenance to maintain performance and durability. In addition,hydraulic fluid may leak, causing damage to the environment (e.g., harmgrass or stain garage floors).

On the other hand, a similar lawnmower using electric propulsioneliminates these challenges and enables new benefits and features. Thelawnmower using electric propulsion and the synchronous inverter mayinclude traction control to prevent one or both wheels from damagingturf, zero radius turning techniques that prevent one wheel fromdamaging turf, optimization of engine speed for a given ground speed asload changes (e.g., uphill, downhill, or in sand), and/or optimizationof engine speed (and fuel consumption) for power take off load changeswhen used in conjunction with electric motor drives.

FIG. 34 illustrates an example subassembly for the vehicle of FIG. 33.FIG. 35 illustrates a reverse view of the example subassembly of FIG.34. FIG. 36 illustrates a top view of the example subassembly of FIG.34.

The subassembly may include the subframe including the support frame 86and the gear frame 87. The support frame 86 is secured to the gear frame87 using one or more connectors. The term connectors as used throughoutmay include any combination of bolts, screws, rivets, or welded joints.Alternatively, the support frame 86 and the gear frame 87 may beintegrally formed. The gear frame 87 is mechanically coupled using oneor more connectors to the gear transmissions. The support frame 86 ismechanically coupled using one or more connectors to the engine 12, thealternator 13, which may include the synchronous inverter 11, and theone or more motors 81.

The subassembly may be pre-assembled as a hybrid power system module.The support frame 86 may be coupled to the chassis of the vehicle usingsupport bars 91. The support frame 86 may include a bracket that slidesonto the support bars 91 and the assembly may be secured to the chassisof the vehicle using one or more connecters. Thus, any combination ofthe engine 12, the alternator 13, the synchronous inverter 11, one ormore motors 81, one or more gear transmissions 82, one or more wheellinkages 83, the support frame 86, and the gear frame 87 may be coupledto vehicle 80 at the same time using the subassembly. In one example,the only mechanical connections between the subassembly and the vehicle80 is made through the support bars 91.

The subassembly may also connect to the vehicle through electricalconnections. The electrical connections may include accessories for thevehicle 80. That is the subassembly, including the alternator 12 or thesynchronous inverter 11, may provide a DC output for running theaccessories for the vehicle 80 such as lights, a radio, a mower decklift, gauges, a control panel, or other features. In one example, highvoltage circuitry associated with the alternator 12 or the synchronousinverter 11 are isolated from the electrical connections between thesubassembly and the vehicle 80. The subassembly may be installed withoutexposure to any high voltage areas. The subassembly may be installed bya user or technician that is not trained in high voltage installations.

The controller 71 determines a drive signal for the load device 75 andgenerates a control signal for the switches of the synchronous inverter11. The synchronous inverter 11 outputs the drive signal, which may bemodified by the output filter 74. The drive signal may include afrequency that specifies a speed of the motor 81. The motor 81 rotates ashaft in the gear transmission 82 at an input speed, and the geartransmission 82 changes the input speed to an output speed. The geartransmission 82 may include a series of gears of different gear ratiosin order to convert from the input speed to the output speed.Alternatively, the motor may be directly coupled to the wheel without atransmission.

The gear transmission 82 may be a right-angle gearbox that transfers themechanical output of electric motor 81 to a drive wheel 85 of thevehicle 80. The gear transmission 82 may include a worm gear fortransferring the direction of rotation of the drive shaft of the motor81 to the direction of rotation of the wheel linkages 83. The wheellinkages 83 are coupled to the drive wheel 85 and apply a rotationalforce to the drive wheel 85.

Optionally, when the gear transmission 82 includes a worm drive gearreduction system, a brake system is not needed because the output shaftis naturally locked unless the input shaft turns. In addition, anoverride clutch may be included in the gear transmission 82 to take oneor more gears out of mesh. When the override clutch is engaged, thedrive wheels 85 are free to operate independently of the geartransmission 82. Thus, when the override clutch is engaged, the vehicle80 may be moved or pushed manually or in tow without the motors 81rotating the gear transmission 82. In another example, the geartransmission 82 may include one or more limited to set a maximum speedfor the drive wheels. Alternatively, the motor may incorporate aspring-applied and electrically-released brake to prevent unintendedmovement of the vehicle 80.

FIG. 37 illustrates a perspective view of the vehicle 80 as a zero turnradius (ZTR) lawnmower. The lawnmower includes drive wheels 85, idlewheels 84, a mower deck 95, and one or more control levers 93. Thesubassembly if FIGS. 34-36 may include a mechanical link to one or morecontrol levers 93 to transfer a user input level as at least one settingfor the motor 91. One or both of the control levers may beinterchangeable with a joystick or another steering mechanism.

Either or both of the control levers 93 may be matched with a positionsensor. The position sensor may include an optical sensor, apotentiometer or resistive sensor, a displacement sensor, or a rotationsensor. As a control lever 93 is rotated forward or backward, theposition sensor determines a direction and amount of the rotation. Theposition sensor may generate an output that is proportional to therotation of the control lever 93. The output of the position sensor foreach control lever 93 is analyzed by the controller 71 to generate acontrol signal for the synchronous inverter 11, which output a drivesignal for motor 81 and corresponding drive wheel 85. The controller 71may determine a position of the control lever 93 from the sensor data.

The controller 71 may include a lookup table that relates positions ofthe position sensor to respective speeds of the motor 81, drive signallevels that correspond to respective speeds of the motor 81, or settingsfor the synchronous inverter 11 that correspond to the respective speedsof the motor 81. The lookup table may be based on the responsiveness ofa hydraulic systems. That is, the lookup table may be selected to causethe controller 71 to mimic a hydraulic system. That is, if a 10 degreerotation in a control lever 93 would result in a 0.5 second delay beforeapplying a target rotation of 20 revolutions per minute in a hydraulicsystem, the lookup table may instruct the synchronous inverter 11 todelay for 0.5 seconds before creating a drive signal that causes themotor 81 to rotate at 20 revolutions per minute. Alternatively, thelookup table may be selected to specify the torque applied to the drivewheel 85, which may mimic a hydraulic system.

The controller 71 may provide a variety of additional controls fortransferring the positional sensor data of the control levers 93 to thedrive signal from the synchronous inverter 11 for driving the motor 81.The additional controls may include a turn setting for turf protection,an incline setting for safety, a steering setting for inclined surfaces,an optimized mowing setting, and a traction control setting.

The turn setting for turf protection may prevent the drive wheels 85from damaging the turf when one wheel is driven and the other is heldstationary. When one wheel is held stationarity, that wheel may spin inplace when the other wheel moves forward. The wheel spinning in placemay damage the turf, pulling grass away from the ground.

The controller 71 may identify this situation and reduce the risk ofdamage. The controller 71 may identify this type of turn (e.g.,potentially turf damaging turn) when one control lever 93 is pushedforward or backward past a threshold position and the other controllever 93 is maintained in a substantially stationary position. An outerwheel of the vehicle 80 corresponds to the control lever 93 is pushedforward or backward past the threshold position, and an inner wheel ofthe vehicle 80 corresponds to the control lever 93 maintained in thesubstantially stationary position. The substantially stationary positionmay be a position deflection of 0 degrees or within a predeterminedrange of 0 degrees. Examples for the predetermined range may includewithin 5, 10, or 15 degrees. Examples of the threshold position to beindicative of forward or backward may be 30, 40, or 50 degrees.

When a potentially turf damaging turn is identified, the controller 71adjusts the control signal for the synchronous inverter 11 and thecorresponding drive signal for the drive wheel 85. The controller 71 maypass the control signal for the one control lever 93 is pushed forwardor backward past the threshold position under normal conditions. Thecontroller 71 may modify the control signal for the wheel in thesubstantially stationary position. The controller 71 may generate thecontrol signal for the synchronous inverter 11 and the correspondingdrive signal for the drive wheel 85 to introduce a nominal adjustment, afeathering, or multiple directional control. The nominal adjustment mayinclude a speed increment or decrement added to the inner wheelassociated with a substantially stationary position. The speed incrementor decrement may be an adjustment in the speed of the inner wheel by thenominal amount (e.g., 1 revolution per minute, or 1 inch per second).Feathering or multiple directional control may include a series ofadjustments to the inner wheel associated with the substantiallystationary position. The controller 71 may cause the inner wheel to beadvanced forward for a first time, rotated backward for a second time,and repeated between forward and backward motion. In addition, thecontroller 71 may include a hysteresis control so that if the useradjusts the control of the inner wheel, which would normally provide thenominal speed or feathering control of the inner wheel, the controller71 maintains the automated speed increment or decrement to the innerwheel rather than that supplied by the user, until the user inputexceeds a threshold set by the hysteresis control.

The controller 71 may provide an incline setting for safety. Thecontroller 71 may receive orientation data from an inertial sensorcoupled to the vehicle 80. The inertial sensor may include anycombination of an accelerometer, a magnetic sensor, or a gyroscope. Theorientation data may describe up to three angles such as roll, pitch,and yaw of the vehicle. The orientation data may include a total angularvalue that describes a sum of the angular difference from the horizontal(e.g., sum of roll angle and pitch angle).

The controller 71 may determine whether the vehicle 80 is travelinguphill or downhill based on at least one of the angles (e.g., pitchangle). The controller 71 may adjust a speed or braking mechanism of thevehicle 80 to reduce the risk of tipping the vehicle 80 or bringing oneor more of the wheels away from the driving surface. The vehicle 80 maybe determined to be driving uphill or downhill when the orientation dataindicates the pitch angle of the vehicle 80 exceeds a threshold (e.g.,greater than a positive angle threshold or less than a negative anglethreshold).

When the vehicle is traveling uphill, when the angle exceeds an uphillthreshold, the controller 71 may adjust the speed for the motor 81 byincreasing the speed of the motor 81 or the speed of the engine 12 byadjusting the control signal for the synchronous inverter 11 and thecorresponding drive signal for the drive wheel 85. When the vehicle istraveling downhill, when the angle exceeds a downhill threshold, thecontroller 71 may adjust the speed for the motor 81 by decreasing thespeed of the motor 81 or the speed of the engine 12 by adjusting thecontrol signal for the synchronous inverter 11 and the correspondingdrive signal for the drive wheel 85.

In addition, the controller 71 may selectively remove current from theelectrical release mechanism of the brake on the wheel (if equipped).The controller 71 may also apply a counter-rotating field to the motorto provide reversing torque. This may be used to load the engine 12 toprevent an engine overspeed condition.

The controller 71 may provide a steering setting for inclined surfaces.The controller 71 may receive orientation data from the inertial sensorcoupled to the vehicle 80. For the inclined surfaces steering, theorientation data may describe the roll angle. When the vehicle travelsalong an incline, the roll angle is substantially nonzero andsubstantially constant. A vehicle traveling along an incline has one setof wheels (e.g., right side) higher in elevation than the other set ofwheels (e.g., left side). The controller 71 may determine that the rollangle is greater than a minimum incline value (e.g., 10 degrees or 5degrees) and consistent with a predetermine variance (e.g., 10% oranother percentage) for a time period. A vehicle traveling along anincline may be a lawnmower traveling perpendicular to a hill.

A ZTR lawnmower traveling along an incline may be particularly difficultto maintain in a forward direction. Due to gravity, the vehicle 80 maytend to veer in the downhill direction. Operators of ZTR lawnmower maydevelop a skill to hold the downhill wheel's control lever at slightlymore of a forward direction than the uphill wheel's control lever. Thecontroller 71 may supplement this control. The controller 71 mayidentify when a user input for forward travel occurs when the roll angleis greater than a minimum incline value and consistent with apredetermined variance for a time period. In response, the controller 71may adjust the speed of the downhill motor to be greater than the speedof the uphill motor. For example, the controller 71 may adjust thecontrol signal for the synchronous inverter 11 and the correspondingdrive signal for the drive wheel 85 of the downhill motor.

When the vehicle 80 is traveling on an incline the controller 71 mayadjust the control signal for the synchronous inverter 11, andeffectively the drive signal for the drive wheels 85 in response to theincline.

The controller 71 may provide an optimized mowing setting based onsensor data for the turf. The sensor data may include a moisture sensorthat detects when wet grass is present. The controller 71 may increase aspeed of the engine 12 in response to the need for increased powerrequired heavier loads like to cut grass that is tall, thick, or wetgrass. Thus, the alternator 13 provides a higher output voltage (if DCmotor) or frequency and/or voltage (if AC motor) to maintain mower bladespeed. Conversely at light loads, the controller 71 would decreaseengine speed. The controller 71 causes the synchronous inverter 11 tomaintain the electrical output to maintain the selected motor speed.

The controller 71 may provide a traction control setting based on sensordata from slippage of the drive wheels 85. For example, each of thedrive wheels 85 may be associated with a speed sensor or position sensorthat tracks the movement of the device wheels 85 and generates dataindicative of the speed or position of the drive wheels 85. Thecontroller 71 compares the speeds and/or positions of the drive wheels85 to determine if one is traveling significantly faster or slower thanthe other. The controller 71 may compare the difference in speed of thewheels to a traction threshold to determine if slippage is occurring.Slippage may occur because of a wet surface (e.g., wet trailer ramps,wet pavement, wet grass), mud, or an unstable surface (e.g., loosestones). In response to determining slippage, the controller 71 mayapply traction control by generating a command for a brake for applyinga braking force to one or more of the drive wheels 85. In one example,the brake force may be applied to the faster (e.g., slipping) wheel.

The controller 71 may adjust the control signal for the synchronousinverter 11 based on characteristics of the motor 81. In one example,physical characteristics may include the structural dimensions of themotor 81 or the amount of metal that makes up the motor 81. Electricalcharacteristics may include the pitch, the number of poles or the numberof windings for the motor 81. The characteristics of the motor 81 maydefine the harmonics produced by the motor 81 or a resonant frequencyfor noise or vibrations produced by the motor 81, adjusting the controlsignal for the synchronous inverter 11 may include adjusting a targetwaveshape to minimize generated harmonics in the motor.

The controller 71 may receive data indicative of the characteristicsfrom a sensor such as a vibration sensor. The controller 81 may receivedata indicative of the characteristics from a user input such as asetting for the model or manufacturer of the install motor 81. Thecontroller 81 may access data indicative of the characteristics from amemory that includes a table of motor models with characteristics.

The characteristics of the motor 81 may be associated with an idealwaveform. The ideal waveform may include a frequency that is tuned tothe particular motor 81. The frequency may be spaced by a set amountfrom the resonant frequency in order to reduce vibration. The frequencymay be selected to reduce harmonics. Using the ideal waveform causes themotor 81 to produce less internal heat, which improved the efficient ofthe system.

The controller 71 may adjust the control signal for the synchronousinverter 11 so that the ideal waveform is applied to the motor 81. Thesubassembly may be assembled before the controller 71 and synchronousinverter 11 are calibrated according to the characteristics of the motor81. In this manner, the harmonics and resonant frequencies for thesubassembly are measured before installation in the vehicle 80, whichfurther reduced the manufacturing burden in assembling the vehicle 80.The calibration eliminates or dampens vibration or harmonics internallyby the subassembly.

A typical inverter (DC to AC or AC to AC) regulates to a root meansquared (RMS) voltage and not a sinusoidal target. Regulating to asinusoidal target allows a subcycle (much faster) response to changes inload on the generator or vehicle. The synchronous inverter 11 mayrespond much more quickly to the changes. The term subcycle refers to achange that occurs in less than a cycle of the drive signal that isoutputted from the synchronous inverter 11.

The controller 71 may implement optimal operation sequences for theengine 12, alternator 13, and synchronous inverter 11 based on thedemands placed by the vehicle 80. For example, the controller 71 mayimplement a hybrid algorithm that switches between power produced at thealternator 13 and energy stored in one or more batteries.

In one example, the controller 71 implements a charging cycle for abattery and the optimal operating characteristic of the least one motor81. The optimal operating characteristics for the engine 12 may be apredetermined percentage (e.g., 80%) of the output of the engine 12 orthe speed of the engine 12. Even when less is demanded by the load, theengine 12 is operating at optimal capacity and any excess is stored inthe batteries. The controller 71 may determine when the one or morebatteries read full charge, or a specific level of charge, and turn offthe engine 12 and alternator 13 and this point. The synchronous inverter11 is then run from the stored energy in the battery until the batteryreaches a minimum level. At this point, the engine 12 is started againand run at the optimal level. The sequence repeats.

The controller 71 may determine an electrical configuration of thesynchronous inverter 11 based on the load connected to the synchronousinverter 11. The electrical configuration may be indicative of a singlephase load or a three phase load. The electrical configuration may be aload characterization indicative of the type of load connected to thesynchronous inverter 11.

The controller 71 may determine whether the load is single phase orthree phase based on a test signal. For example, consider three outputsfor the synchronous inverter (A, B, C). The controller 71 may send atest voltage to one of the outputs (A) and measure the resulting voltageon one or more of the other outputs (B, C). When the other outputs (B,C) are measured at a level substantially similar to the test voltage,the controller 71 determines that the load is single phase. Otherwise,the controller 71 determines that the load is three phase.

The controller 71 also may determine the type of load based on a testsignal. Example types of load include resistive, nonlinear, capacitive,inductive, and reactive. Example nonlinear loads include batterychargers, uninterruptible power system (UPS), or variable frequencydrives (VFD). The controller 71 is configured to adjust the gains of thesynchronous inverter 11 through the states of the switches in thecontrol signal in response to a load characterization of a load of thesegmented waveform converter.

The controller 71 may identify subcycle load changes based on the typeof load. For example, nonlinear loads may include a load spike thatoccurs at a particular time in the cycle. The load spike may occur whena SCR fires at a particular subcycle position (e.g., 60 degrees). Thecontroller 71 may modify the control signal for the synchronous inverter11 so that the output of the synchronous inverter increases at apredetermined time (e.g., a set number of milliseconds) or a setposition in the cycle before the predicted load spike. The pre-emptivechange in output may reduce the dip in power that could occur after theload spike. A similar control may be applied to the reduction of a load,avoiding the overshoot in power.

As described above in associated with FIGS. 19-28, multiple synchronousinverters may be linked together to provide power to a load in parallel(providing increased current output) or in series (providing increasedvoltage output). The synchronous inverters may also communicate with oneanother using a synchronizing signal in order to match phase angleacross different inverters, adjusting their supply voltage using thecommunications network. In addition or in the alternative, thecontroller 71 may generate a communication signal that is modulated onthe output drive signal of the synchronous inverter 11 by acommunication interface. The communication signal may be a highfrequency signal encoded with data using frequency modulation or pulsewidth modulation. The modulated communication may be high enough infrequency so as to not interrupt the operation of the motors or otherload but still detectable by controllers for the other synchronousinverters in the system.

The synchronous inverters may communicate in order to equalize loadingand ensure equal wear among a group of connected synchronous inverters11. For example, for a 25 kW load and four synchronous inverters, theinverters may communicate their loads so that each synchronous inverterconverges to supplying 6.26 kW to the load.

FIG. 38 illustrates a flow chart for the operation of the controller 71,which may be implemented by the generator controller of FIG. 16.Additional, different or fewer acts may be included.

At act S301, the processor 300 is configured to receive, at an inputcoupled to a controlled field alternator, a feedback signal. Thefeedback signal may be indicative of the current output of thecontrolled field alternator. The processor 300 may access a targetoutput from memory 352 or receive the target output from communicationinterface 353 from workstation 359 or another synchronous inverter.

At act S303, the processor 300 generates a drive signal for at least onemotor at a segmented waveform converter or synchronous inverterincluding switches connected to the feedback signal of the controlledfield alternator. At act S305, the processor 300 modifies the drivesignal based on at least one setting for the motor. At least one settingmay include physical parameters of the load motor, a tilt setting fortraveling on an incline, a decline, or along an incline, a turn settingfor low radius turns, a load setting for the motor, a fuel efficiencysetting, or a configuration setting.

FIG. 39 illustrates an example set of inverters 301 a-c connected to analternator 313 for driving a motor 303 in a wye configuration. FIG. 40illustrates an example set of inverters 301 a-c connected to thealternator 313 for driving a motor 303 in a delta configuration. Otherconfigurations such as high wye or low wye may be used.

The alternator 313 provides three three-phase bundles 302 a-c eachhaving three phase connections (i.e., bundle 302 a includes three phasesfor the input of inverter 301 a, bundle 302 b includes three phases forthe input of inverter 301 b, and bundle 302 c includes three phases forthe input of inverter 301 c).

Each of the set of inverters 301 a-c generator provides one phase to themotor 303. For example, as described above each of the inverters mayinclude an input coupled to a controlled field alternator and configuredto receive a polyphase signal from the controlled field alternator and asegmented waveform converter including switches connected to thepolyphase signal of the controlled field alternator and generate a drivesignal for at least one motor. The segmented waveform converter includesa network of switches that selectively controls passing a combination ofthe components of the poly-phase signal to the output. The combinationis switched multiple times per cycle. When the polyphase signal includestwo components, A and B, example combinations include only the Acomponent, only the B component, an additive signal of A+B, a subtractedsignal of A−B or B−A, and 0 or a null signal, which may be achieved byA−A or B−B.

FIGS. 41-44 illustrate various hybrid arrangements of a set of invertersfor driving a load. FIG. 41 illustrates a set of inverters 301 a-d fordriving a motor 303. An example application is a hybrid lawnmower or ahybrid zero turn radius lawnmower. The alternator 313 and the battery312 supply power to the motor 303 from the set of inverters 301 a-d. Inaddition, the alternator 313 may charge the battery 312 directly orthrough the motor 303. A switch 306 (e.g., a relay) may be configured toswitch the inputs of the inverter between the battery 312 and thealternator 313. In one example, the switch 306 in integrated into theinvertor circuit.

The set of inverters 301 a-d may be included in package 301. The package301 may be a supporting enclosure or case that supports thesemiconductors or other electronics that make up the set of inverters301 a-d. The package 301 may include a series of pins corresponding tothe inputs and outputs of the set of inverters 301 a-d. Any of theinverters described here may be embodied in a single combined package oran individual package for each inverter.

In the hybrid arrangement of set of inverters 301 a-d for driving amotor 303, the battery 312 may provide power the motor 303 and thealternator 313 may provide power to the motor 303 in varying proportion.The battery 312 may provide power to the alternator 313 to start theengine. The alternator 313 may provide power to charge the battery 312.

The alternator 313 may provide one, two, or three phases to the motor303. The alternator 313 may provide one or two phases and the battery312 provides the other phase. The battery 312 may provide two phases tothe motor 303, through inverter circuit 301 c and inverter circuit 301d, and the third phase is provided by closing switches in invertercircuit 301 a so that current flows. In this case, the motor 303 ispowered at reduced power (i.e., less than rated power). This is anunderrated operating condition of the motor 303.

FIG. 45 illustrates an example of the motor 303 having two phasesconnected to voltage sources (e.g., inverter circuit 301 c and 301 d)and the third phase connected to a current sink (e.g., inverter circuit301 a). The arrangement of two voltage sources connected to a motor,which is connected to a current sink, may be referred to as a biphasemotor. The motor 303, provided with power from two phases (e.g.,inverter circuit 301 c and 301 d), may still operate (e.g., rotate)under the power from two phases. The excitation from two of the phasescauses the motor to generate the third phase as long as there is a pathfor the current to flow. The output of a biphase motor may be less thanthat of a fully powered three phase motor. In one example, when a threephase motor operates at 80-90% efficiency, a corresponding biphase motormay operate at 70-80% efficiency. In one example, the minimum efficiencyof the biphase motor is about 67% and the biphase motor provides fullrated torque. The hybrid arrangement of the set of inverters 301 a-d mayprovide a biphase motor by connecting two phases of motor 303 to asource (e.g., battery 312, alternator 313, or a combination thereof)through two of the inverters 301 a-d and one phased of the motor to asink through another of the inventors 301 a-d.

On the other hand, the motor 303 may operate in an overrated conditionwith all four of the inverter circuits 301 a-d. For example, thealternator 313 may provide power to the motor 303 through both theinverter circuit 301 a and the inverter circuit 301 c, and the batterymay provide power to the motor 303 through both the inverter circuit 301c and 301 d. In this example, ⅔ of the rated current of the motor 303may be provided by the alternator 213 and ⅔ of the rated current of themotor 303 may be provided by the battery 312.

Any of the set of inverters 301 a-c may be referred to as firstinverter, second inverter and so on. One example includes a firstinverter circuit 301 a, a second inverter circuit 301 b, a thirdinverter circuit 301 c, and a fourth inverter circuit 301 d. The firstinvertor circuit 301 a is configured to couple the alternator 313 andthe motor 303 to deliver a driving signal from the alternator 313 to theload device 303. The driving signal may include components of differentphases of the output of the alternator 313 that are summed or subtractedfrom each other according to switches in the inverter circuit 301 a.

Each of the inverters, or any combination thereof, may be connected tothe battery on either the output side (right side, or motor side in FIG.41) or the input side (left side, or alternator side in FIG. 41). On theinput side the battery terminals may be connected to phases of one ofthe bundles of conductors coupled with the alternator 313. The negativeterminal of the battery may be connected to two of the phases and thepositive terminal of the battery may be connected to the other phase. Onthe output side the output side, the terminals of the battery areconnected to the output, optionally through diodes, and to one of thephases of the motor 303. An inverter with the battery 312 connected onthe output side (e.g., inverter circuit 301 b) charges the battery 312or the battery 312 is charged through the motor 303. An inverter withthe battery 312 connected on the input side is powered by the battery312. Different batteries may be coupled to different inverters.

The second invertor circuit 301 b is configured to couple the alternator313 to the motor 303 to deliver a driving signal from the alternator 313to the motor 303 in some instances, and also configured to couple thebattery 312 to the alternator 313 to deliver a charging signal from thealternator 313 the battery 312.

When providing the driving signal to the motor 303, the second invertercircuit 301 b receives an AC signal from the alternator 313 andgenerates another AC signal, which may be a different frequency than theAC signal received from the alternator 313.

The second inverter circuit 301 b is configured to couple the battery tothe load device to deliver a charging signal from the motor 303 to thebattery 312. When providing the charging signal to the battery 312, thesecond inverter circuit 301 b still receives the AC signal from thealternator 313 but generates the charging signal for the battery 312.The charging signal may still be an AC signal but may be a much higherfrequency. In one example, the charging signal generated by the secondinverter circuit 301 b, which is electrically connected to invertercircuit 301 d, is provided through inverter circuit 301 d to the battery213. The higher frequency may be a predetermined frequency or anyfrequency above a predetermined frequency. Examples for thepredetermined threshold may be 1 kHz, 2 kHz, or another value. Becauseof the impedance of the motor 303, the higher frequency signal does notsubstantially affect the operation of the motor 303.

The second inverter circuit 301 b is configured to couple the battery312 to the alternator 313 to deliver a cranking signal from the motor303 to the battery 312 to an engine coupled to the alternator 313. Theinverter 301 b may be used to crank the engine or initiate enginerotation by converting battery power from battery 313 provides an ACvoltage waveform on the alternator stator windings. The resultingrotating magnetic flux in the stator applies a torque on the rotor. Thetorque causes the engine to spin, causing air and fuel to be compressedin the cylinders and allowing the engine to initiate combustion, whichstarts the engine.

A third inverter circuit 301 c is configured to couple the battery 312to the motor 303 or couple the alternator 313 to the motor 303 todeliver a second driving signal to the motor 303. A fourth invertercircuit 301 d is configured to couple the battery 312 to the motor 303to deliver a third driving signal from the battery 312 to the motor 303.

FIG. 42 illustrates a hybrid arrangement of a set of inverters 301 a-dfor driving a load 304. Each of the inverter circuits are connected tothe battery 312. Inverter circuits 301 a and 301 b are connected to thebattery 312 on the output side for charging the battery from the load304. Inverter circuits 301 c and 301 d are connected to the battery 312on the input side for charging the battery from the alternator 313and/or providing power to the load 304. Alternatively, differentbatteries may be connected to different inverter circuits.

The battery 312 provides power to the load 304 in various scenarios. Thecontroller (e.g., controller 91 or controller 200) may switch one ormore of the inverters circuits 301 a-301 d to connect the battery 312 tothe load 304 based on a user input, a control schedule, or based on thecurrent level of the battery 312. For example, the battery 312 mayprovide power to the load 304 until the battery 312 falls below apredetermined level. At this point, the battery 312 may also beconnected to the alternator 313 to crank the engine by one or more ofthe inverters circuits 301 a-301 d. In one example, power flows throughthe set of inverters 301 a-d in two directions in order to start thegenerator set. For example, power may flow from battery 312 to the load304 through inverter circuits 301 c and 301 d in a first direction andback from the load 304 through invert circuits 301 a and 301 b to startthe engine.

One or more of the inverters circuits 301 a-301 d may be overloaded fora short period of time, placing a burden on the heat sink, but theoverloading and burden is only temporary. In this case, temporary meansa predetermined amount of time (e.g., about one second to a few secondsor up to 30 seconds) sufficient to start the generator set. In responseto the generator set running, the inverters circuits 301 a-301 d returnto normal load.

FIG. 43 illustrates a simplified hybrid arrangement for the set ofinverters 301 a-d for driving a motor 303. In the embodiment of FIG. 43,as compared to the embodiment of FIG. 41, no battery is connected toinverter circuit 301 b. Therefore, at least one fewer switching circuitor relay is required. In the embodiment, because no switching isrequired for any of the inverter circuits, no relays or switchingcircuits may be included. FIG. 43 illustrates an embodiment for the setof inverters 301 a-d with an absence of relays and contactors.

In the embodiment of FIG. 43, the inverter circuit 301 d may generate adriving signal for motor 303 at a high frequency. Example highfrequencies includes 1 kHz, 5, kHz, and 10 kHz. The motor 303 is aconductive path for the high frequency driving signal to pass in areverse direction through inverter circuit 301 b or inverter circuit 301a to the alternator 313 for starting the engine.

FIG. 44 illustrates another simplified hybrid arrangement of a set ofinverters 301 a-d for driving a motor 303. The embodiment of FIG. 44, ascompared to the embodiment of FIG. 43, does not include a connection tothe alternator 313 to the inverter circuit 301 c. Therefore, at leastone fewer switching circuit or relay is required as compared to FIG. 43,or at least two fewer switching circuits or relays are required ascompared to FIG. 41.

In FIG. 44, the battery 312 may be charged through either invertercircuit 301 c or inverter circuit 301 d, which generate a DC signal orhigh frequency AC signal from motor 303, which is powered by alternator313 through inverter circuit 301 a and inverter circuit 301 b. Thealternator 313 may drive the motor 303 through inverter circuit 301 aand inverter circuit 301 b. In addition, the battery 312 may supplementthe alternator 313 through either inverter circuit 301 c or invertercircuit 301 d.

FIGS. 46-51 illustrate block diagram representations of a set ofinverters 301 a-d for driving a motor 303. The set of inverters 301 a-dmay be controlled by a generator controller (e.g., controller 91 orcontroller 200), described herein and including at least processor 300,memory 352, and communication interface 353. Additional, different, orfewer components may be included.

The controller may select a position of switch 320 and the positions ofswitches, which may include at least one energy storing device, in theset of inverters 301 a-d. The position of switch 320 may either be at anengine/alternator setting (i.e., the load 303 is connected by the switch320 to the alternator 313) or a battery setting (i.e., the load 303 isconnected by the switch 320 to the battery 312). The battery setting isconductive to allow a current from the battery 312 to the invertercircuit 301 b. The engine/alternator setting is conductive to allow acurrent from the inverter circuit 301 b to the battery 312.

FIG. 46 illustrates an example battery mode for operation of a motorpowered by battery 312 in which the switch 320 is in the batterysetting. The engine and alternator 313 may be off in the battery mode.Battery 312 provides power through inverter circuit 301 b, in theforward direction, to a first phase of the motor 303, and the battery312 provides power through inverter circuit 301 d, in the forwarddirection, to a second phase of the motor 303. The inverter circuit 301a may be a current sink in the battery mode, and the inverter circuit301 c may be an open circuit or otherwise unused in the battery mode.For an inverter circuit to be an open circuit, one or more switches maybe open. In one example, all switches of the inverter circuit are open.In another example, at least enough switches are open such that no pathis complete through the inverter circuit. For the inverter circuit tosink current, the inverter circuit closes switches for that phase of themotor. The inverter circuit may be commutating for a particular phase.

FIG. 47 illustrates an example engine mode for hybrid operation of themotor 303 in which all power originates with the engine and alternator313 and the battery 312 is charged from the alternator 313. The switch320 is in the engine setting. Each of inverter circuits 301 a-cgenerates a different drive signal for a different phase of the motorand each may operate in the forward direction. Power flows from themotor 303 through inverter circuit 301 d to charge the battery 312 inthe reverse direction.

FIG. 48 illustrates an example maximum power mode for hybrid operationof the motor 303. The switch 320 is in the battery setting. The motor303 receives power in a first phase and third phase through invertercircuit 301 a and inverter circuit 301 c in the forward direction. Themotor 303 receives power in a second phase and the third phase throughinverter circuits 301 b and 301 d from the battery 312 in the forwarddirection. The maximum power mode may provide more than a rated power tothe motor 303. For example, up to ⅔ of the rated power may be providedby the battery 312 and up to ⅔ of the rated power may be provided by thealternator 313.

FIG. 49 illustrates an example crank while driving mode for hybridoperation of a motor. The switch 320 is in the engine setting. The motor303 receives a high frequency cranking signal from inverter circuit 301b and/or inverter circuit 301 d in the forward direction. The motor 303provides the high frequency inverter signal through inverter circuit 301a and/or inverter circuit 301 c in the reverse direction.

FIG. 50 illustrates an example regenerative mode for hybrid operation ofa motor. The switch 320 is in the battery setting. Power from the wheelsof the vehicle is converted to electrical energy by motor 303. Theinverter circuit 301 b and/or 301 d provides a charging signal to thebattery 312 in the reverse direction. The inverter circuit 301 c may bean open circuit or otherwise inactive in the regenerative mode. Theinverter circuit 301 a may be a current sink to provide a path for themotor 303 driven by the inverter circuits 301 b and/or 301 d.

FIG. 51 illustrates an example maximum braking mode for hybrid operationof a motor. The switch 320 is in the reverse direction. The motor 303returns power to the system, which is provided to both the battery 312and the alternator 313.

Table 3 illustrates the settings of the switch 320 and the inverters 301a-d.

Inverter Inverter Inverter Inverter Mode FIG. 301a 301b 301c 301d Switch320 Battery FIG. 46 Sinking Forward Open Forward Battery current EngineFIG. 47 Forward Forward Forward Reverse Engine Maximum FIG. 48 ForwardForward Forward Forward Battery power Cranking FIG. 49 Reverse ForwardReverse Forward Engine Regenera- FIG. 50 Sinking Reverse Open ReverseBattery tive current Maximum FIG. 51 Reverse Reverse Reverse ReverseBattery braking

FIG. 52A illustrates a series hybrid drive system for the inverter 301in the vehicle 342. FIG. 52B illustrates a parallel hybrid drive systemfor the inverter 301 in the vehicle 342. Both systems include an engine331, an alternator 333, a battery 307, an inverter circuit 301, and amotor drive system 305 coupled to at least one wheel 343. Additional,different, or fewer components may be included.

In the series hybrid drive system, the engine 331 is not mechanicallycoupled to the driven load (e.g., wheel 343). Instead, mechanical poweris transferred from the engine 331 to the generator 333 and converted toelectrical energy which is modified by the inverter 301, which providespower to the driven load (e.g., wheel 343) via the motor drive system305. In the parallel hybrid drive system, there is a mechanicalconnection between the engine 331 and motor drive system 305 in additionto the mechanical connection to the generator 333.

In one embodiment, the inverter circuit 301 is configured for anemergency mode, which may be referred to as battle mode or limp homemode. Consider to vehicles 342 traveling together, and at least one ofthe vehicles (“limited vehicle”) is presently relying on storedelectrical power (e.g., battery). The limited vehicle may have run outof fuel, rendering the engine 331 unavailable. The limited vehicle mayonly have electrical power. The inverter circuit 301 of the vehicle maybe connectable using an external cable (e.g., extension cord). Thus, thelimited vehicle receives elected power from the inverter circuit 301 ofthe other vehicle, which operates the motor drive system 305. Tetheredtogether, the vehicles 342 are able to limp home together under limitedpower. In some examples, the limited example may have a malfunctioningor missing inverter circuit 301, and the inverter circuit 301 of theother vehicle is connected directly to the motor drive system 305 of thelimited vehicle.

FIGS. 54A and 54B illustrates an example marine application for theinverter. FIG. 54A illustrates a series hybrid drive system for theinverter 301 in the marine vehicle 442. FIG. 54B illustrates a parallelhybrid drive system for the inverter 301 in the marine vehicle 442. Themarine vehicle 442 may include a boat, a submersible craft, a fan boat,or another vehicle. The descriptions of the engine 331, the alternator333, the battery 307, the inverter circuit 301, and the motor drivesystem 305 described with respect to FIGS. 52A and 52B apply to themarine vehicle 442. The motor drive system 305 is mechanically coupledto the propulsion device 443, which may include a propeller, animpeller, a fan, or similar device to propel the marine vehicle 442 viawater. Additional, different, or fewer components may be included.

FIG. 53 illustrates an example light tower 701 application for theinverter. The invertor 301 applied to a light tower 701 include one ormore light sources powered by the generator 333 through inverter circuit301. The light tower 701 may include a structure that is extendible atvariable distances above the ground and supporting the one or more lightsources. The output of the generator 333 may be modified by the invertercircuit 301 for different applications. The inverter circuit 301 maycontrol the intensity of the light(s) of the light tower 701. In highoutput applications, a first drive signal is generated for the lighttower 701, and in low output application, a second drive signal isgenerator for the light tower 701.

The inverter circuit 301 may include multiple portions corresponding tomultiple inverter circuits 301 a-d as described in embodiments herein.Various effects may be provided by connecting the different at differentlights (e.g., light emitting diodes or LEDs) at different arrangementsor colors. The lights may form a sign including text or images formed bythe LEDs.

Considering four inverter circuits 301 a-d, in one embodiment invertercircuit 301 a may correspond to red LEDs, inverter circuit 301 b maycorrespond to green LEDs, inverter circuit 301 c may correspond to blueLEDs, and inverter circuit 301 d may correspond to an AC output. Inanother embodiment, inverter circuits 301 a-c may correspond to a threephase AC output (e.g., for powering a load such as a motor), andinverter circuit 301 d may correspond to a DC output for the light tower701 with varying intensity levels. Other quantities and arrangements ofinverter circuits are possible. The battery 307 may provide power to thelight tower 701 and/or be charged by the generator 333 and described inthe operation modes shown in FIGS. 46-51.

FIG. 55 illustrates a doubly fed machine 500 for the inverter. Thedoubly fed machine 500 includes an exciter portion 508 and a maingenerator portion 510. The exciter portion 508 includes permanentmagnets 511, an exciter field 512, exciter armature laminations 515, andexciter armature windings 516. The main generator portion 510 includes astator 513, a rotor 514, rotor laminations 517 a, stator laminations 517b, rotor windings 518 a, stator windings 518 b, a cooling fan 520 anddrive plates 521. Additional, different, or fewer components may beincluded.

Cross section A illustrates the relative position of inverters 501,which are mounted to the rotor 514, as a rotating circuit board orrotating inverter package. In this embodiment, the inverters 501generate a rotating magnetic field and may be referred to as a rotatingfield generator and/or a magnetic flux sourcing device.

The cooling fan 520 pushes air across the rotor windings 518 a andstator windings 518 b to cool the generator. The cooling fan 520 pushesair across the inverters 501 for cooling.

The inverters 501 may each generate a phase for the field current. Theinverters 501 may receive a target output frequency and control thefield current in order to set the rotating field current. The targetoutput frequency may be set by an internal configuration setting (e.g.,stored as a value in memory). The target output frequency may bereceived from an external device. The inverter 501 may detect the speedof the engine, or calculate the speed of the engine, based on thepassing speed of the permanent magnet 511. When the speed of the engineis different that the target output frequency, the inverter 501 maydetermine a superposition frequency based on the difference. Theinverter 501 adjusts the field current according to the superpositionfrequency to supplement the speed of the engine. By adjusting the fieldcurrent, the output of the doubly fed machine 500 may vary independentlyfrom the speed of the engine. The superposition frequency may be anon-integer multiple of a mechanical frequency of the alternator.

In one example, the engine and alternator may be driven at 1600 rpm. Theinverter 501 identifies a target speed of 1800 rpm, which corresponds toa target frequency of 60 Hz for alternator with two poles. The inverter501 detects that the speed of the alternator is less than the targetspeed and determines a superposition frequency of 60/9 or 6.66 Hz orsuperposition speed corresponding to 200 rpm. The inverter 501 generatesa field current having the rotating field at the superposition frequencyto supplement the alternator. In effect, the supposition frequency issummed with the initial output of the alternator to reach the targetfrequency.

FIG. 56 illustrates an example a flow chart for operating the invertercircuit using a controller, which may be implemented by the generatorcontroller of FIG. 16. Additional, different or fewer acts may beincluded.

At act S401, the controller identifies a target frequency for analternator. The target frequency may be received from a user input. Thetarget frequency may be identified from a switch or jumper in electricalconnection to the controller. The target frequency may be received overa network from another device. The target frequency may be adjusted overtime.

At act S403, the controller detects a current speed of the alternator.The speed of the alternator may be detected by detecting the movement ofthe rotor. For example, a magnetic sensor may detect how many timesand/or how often a magnet or a coil based the sensor. In anotherexample, the speed of the alternator may be detected from an electricparameter sensor measuring the current or voltage output of thealternator. The speed may be inferred from a control signal thatinstructs the speed of the engine.

At act S405, the controller calculates a supplemental frequency based onthe target speed and the current speed. The controller may calculate adifference speed the absolute value of the difference between the targetspeed and the current speed. The difference speed is compared to thetarget speed to calculate a ratio. The ratio is applied to (e.g.,multiplied by) the target frequency to calculate a supplementalfrequency.

At act S407, the controller receives a poly-phase signal from thealternator. At act S409, the controller generates a field current basedon the supplemental frequency. The field current may have a frequencyequal to the supplemental frequency. The field current may have afrequency that is a predetermined fraction of the supplemental frequencyor a predetermined multiple of the supplemental frequency. The fieldcurrent may be generated using a segmented waveform converter includingthe switches connected to the poly-phase signal of the alternator asdescribed in any embodiment herein.

In another embodiment, the synchronous inverter according to any of theprevious embodiments may be applied to a generator load banking device.The generator load banking device may be configured to test thegenerator by applying a load to the generator and dissipating theresultant output of the generator. The load may be select to respondsimilar to a typical load such as a heater, a motor, refrigeration,lights, or another load.

FIG. 57 illustrates a load banking device. The synchronous inverter maybe configured to provide load adjustments on a generator load bankingdevice. A load bank is a collection of resistive or reactive elementsutilized for testing a generator. Typically, each element has a relay orcontactor associated with it to provide control. For example, there maybe a set number such as 20 parallel connected resistive elements in a100 kW load bank of different magnitudes that can be switched on or offto provide load at a desired power level. The desired power level may be57 kW and require actuating a set number such as 14 of the relays orcontactors. If a synchronous inverter is connected between the generatorand the load elements, the system may be lower cost and more reliable.Utilizing the synchronous inverter, a single resistive or reactiveelement can be utilized and leveraged for load selection by adjustingthe synchronous inverter output voltage up or down. For example, in a100 kW load bank at 480V, a single resistive element of 2.3 ohms can beused on each phase. To configure a load of 57 kW, the input to thesynchronous inverter from the generator would remain 480V, but thesynchronous inverter output would be targeted to 362V into the 2.3 ohmload. This eliminates the cost and complexity of the relays andcontactors.

A generator is used to supply power to a building or facility. Loads ina building or facility may include relatively constant loads (e.g.lighting) that do not change over the course of minutes or hours,periodic loads (e.g. refrigeration compressors) that turn on and offover the course of minutes or hours, and non-linear loads (e.g. variablefrequency drives) that turn on and off over the course of an electricalcycle. Typically, a load bank is utilized to provide a buildingequivalent load to the generator that does not change. A load bank is agood representation of a constant load but a poor representation of aperiodic or non-linear load. The contactors or relays used to switchelements in and out of the load circuit do not switch fast enough torepresent a non-linear load and, being mechanical devices, have alimited number of actuations over the course of their lifetime. Thecontactors and relays cannot readily be switched to represent anon-linear load and would suffer a short lifespan in representing aperiodic load. By utilizing the synchronous inverter between thegenerator and the load bank, the relays and contactors are eliminated,and the full range of load types may be represented. Further, if theloads in the building are known, the synchronous inverter may beprogrammed with a load profile that is representative of the building orfacility load to load the generator in a more representative fashion,including profiles that provide a worst case plurality of periodic andnon-linear loads (e.g. there may be a time when a plurality of loadswill turn on simultaneously and look like a single, much larger load tothe generator).

A load bank is typically utilized for commissioning testing (beforesupplying power to a building or facility) or maintenance testing atperiodic intervals (e.g. quarterly, annually) of a generator. It is usedto load the generator without having a building or facility relying onpower from the generator. Typically, this is done with resistive (e.g.resistors) or reactive (e.g. inductors) elements. Using the synchronousinverter, it is possible to use the utility grid to provide a load tothe generator and exclude the use of resistive or reactive elementsaltogether. This may lower the cost and size of a loading apparatus andallow the generator power to be sold to the utility. FIG. 57 shows anexample system. FIG. 57 shows a 3 phase generator 601 connected to asynchronous inverter 602. The output of the synchronous inverter 602feeds the primary side of a 3 phase transformer 603 with isolatedwindings. The transformer 603 has its secondary side connected to theutility grid. In this example, the nominal voltage output from thegenerator 601 is 208V line to line, the line to neutral nominal voltageoutput from the synchronous inverter 602 is 120V, and the line toneutral nominal voltage on the utility is 277V. The synchronous inverter602 is used as a current phase and current amplitude controlling deviceto control the amount of power the generator 601 is delivering to theutility; for a given target current, the voltage output from thesynchronous inverter 602 is adjusted up or down to respectively increaseor decrease load on the generator 601. For example, to have no load onthe generator, the synchronous inverter may control current to 0. Thevoltage observed on the primary side of the transformer 603 would be120V line-to-neutral, generated by the utility voltage. For example, tohave load on the generator 601, the synchronous inverter 602 mayincrease voltage on the primary side of the transformer 603 until acommanded current output from the generator 601 is reached; thisincreased voltage may be 122V line to neutral on the primary oftransformer 603. The commanded current may incorporate an amplitude andphase element to accommodate both real and reactive power elements.

The processor 300 may include a general processor, digital signalprocessor, an application specific integrated circuit (ASIC), fieldprogrammable gate array (FPGA), analog circuit, digital circuit,combinations thereof, or other now known or later developed processor.The processor 300 may be a single device or combinations of devices,such as associated with a network, distributed processing, or cloudcomputing.

The memory 352 may be a volatile memory or a non-volatile memory. Thememory 352 may include one or more of a read only memory (ROM), randomaccess memory (RAM), a flash memory, an electronic erasable program readonly memory (EEPROM), or other type of memory. The memory 352 may beremovable from the network device, such as a secure digital (SD) memorycard.

In addition to ingress ports and egress ports, the communicationinterface 303 may include any operable connection. An operableconnection may be one in which signals, physical communications, and/orlogical communications may be sent and/or received. An operableconnection may include a physical interface, an electrical interface,and/or a data interface.

The communication interface 353 may be connected to a network. Thenetwork may include wired networks (e.g., Ethernet), wireless networks,or combinations thereof. The wireless network may be a cellulartelephone network, an 802.11, 802.16, 802.20, or WiMax network. Further,the network may be a public network, such as the Internet, a privatenetwork, such as an intranet, or combinations thereof, and may utilize avariety of networking protocols now available or later developedincluding, but not limited to TCP/IP based networking protocols.

While the computer-readable medium (e.g., memory 352 or database 357) isshown to be a single medium, the term “computer-readable medium”includes a single medium or multiple media, such as a centralized ordistributed database, and/or associated caches and servers that storeone or more sets of instructions. The term “computer-readable medium”shall also include any medium that is capable of storing, encoding orcarrying a set of instructions for execution by a processor or thatcause a computer system to perform any one or more of the methods oroperations disclosed herein.

In a particular non-limiting, exemplary embodiment, thecomputer-readable medium can include a solid-state memory such as amemory card or other package that houses one or more non-volatileread-only memories. Further, the computer-readable medium can be arandom access memory or other volatile re-writable memory. Additionally,the computer-readable medium can include a magneto-optical or opticalmedium, such as a disk or tapes or other storage device to capturecarrier wave signals such as a signal communicated over a transmissionmedium. A digital file attachment to an e-mail or other self-containedinformation archive or set of archives may be considered a distributionmedium that is a tangible storage medium. Accordingly, the disclosure isconsidered to include any one or more of a computer-readable medium or adistribution medium and other equivalents and successor media, in whichdata or instructions may be stored. The computer-readable medium may benon-transitory, which includes all tangible computer-readable media.

In an alternative embodiment, dedicated hardware implementations, suchas application specific integrated circuits, programmable logic arraysand other hardware devices, can be constructed to implement one or moreof the methods described herein. Applications that may include theapparatus and systems of various embodiments can broadly include avariety of electronic and computer systems. One or more embodimentsdescribed herein may implement functions using two or more specificinterconnected hardware modules or devices with related control and datasignals that can be communicated between and through the modules, or asportions of an application-specific integrated circuit. Accordingly, thepresent system encompasses software, firmware, and hardwareimplementations.

We claim:
 1. An apparatus comprising: a controlled field alternatorconfigured to generate a polyphase signal; a plurality of switchesconnected between the polyphase signal of the controlled fieldalternator and an output filter; and a controller configured to providea control signal for the plurality of switches based on an output of theoutput filter and provide a field current control signal to thecontrolled field alternator.
 2. The apparatus of claim 1, wherein thecontrolled field alternator is a wound field alternator.
 3. Theapparatus of claim 2, wherein the wound field alternator is a dual axisalternator with a main stator device and an exciter field device on acommon plane normal to an axis of rotation.
 4. The apparatus of claim 1,wherein the controller is configured to calculate a plurality ofcombinations of available voltages through different settings for theplurality of switches, and the field current control signal includes atleast one of the plurality of combinations.
 5. The apparatus of claim 4,wherein one of the plurality of combinations is for starting an enginecoupled to the controlled field alternator by a reverse flow through aconverter including the plurality of switches.
 6. The apparatus of claim1, wherein the control signal is a pulse width modulated (PWM) signal.7. The apparatus of claim 1, wherein the plurality of switches includesa first switch associated with a first output range and a second switchassociated with a second output range.
 8. The apparatus of claim 1,wherein the controller is configured to generate a start signal to startan engine associated with the controlled field alternator.
 9. Theapparatus of claim 1, further comprising: a battery circuit electricallyconnected to the plurality of switches and a battery.
 10. The apparatusof claim 9, wherein the battery circuit is configured to provide acranking signal to an engine associate with the controlled fieldalternator.
 11. The apparatus of claim 1, further comprising: an enginecoupled to the controlled field alternator, the engine configured tooperate at a fixed speed.
 12. A method comprising: generating apolyphase signal at a controlled field alternator; determining an outputcontrol signal to control a plurality of switches connected between thepolyphase signal of the controlled field alternator and an outputfilter; and determining a field current control signal to control afield current of the controlled field alternator.
 13. The method ofclaim 12, further comprising: sending the output control signal to aload; and providing the field current control signal to a generatorcontroller.
 14. The method of claim 12, further comprising: calculatinga plurality of combinations of available voltages through differentsettings for the plurality of switches, wherein the field currentcontrol signal includes at least one of the plurality of combinations.15. The method of claim 12, wherein the output control signal is a pulsewidth modulated signal.
 16. The method of claim 12, wherein theplurality of switches includes a first switch associated with a firstoutput range and a second switch associated with a second output range.17. The method of claim 12, further comprising: generating a startsignal to start an engine associated with the controlled fieldalternator.
 18. A method comprising: generating a polyphase signal at acontrolled field alternator coupled to an engine configured to operateat a fixed speed; determining an output control signal to control aplurality of switches connected between the polyphase signal of thecontrolled field alternator and an output filter; and determining afield current control signal to control a field current of thecontrolled field alternator.
 19. The method of claim 18, wherein thecontroller is configured to generate a start signal to start an engineassociated with the controlled field alternator.
 20. The method of claim18, wherein the fixed speed is greater than a corresponding frequency ofan output of the output filter.